C11.Haematology

Anaemia occurs when the level of functional haemoglobin in the blood falls below the reference level appropriate to the sex and age of an individual. Alternatively, anaemia can be defined as a reduction in red blood cell count or in the packed cell volume.

Anaemia is a major world public health problem, due to poor diet, chronic diseases, wars and famine: this chapter considers the more common causes. It does not deal with anaemia due to sudden bleeding.

Bone marrow failure is discussed briefly, as a basis for understanding the use of new biolog-

ical agents. The clotting system and the management of anticoagulation is covered in the final

section.

Some other aspects of haematology (e.g. leukaemias) are covered in Chapter 10, clotting

problems affecting the cardiovascular system in Chapter 4 and some aspects of blood transfusion

in Chapter 2.

Red blood cell production and function

Erythpoiesis

Mature red blood cells (RBCs, erythrocytes) are

biconcave discs 7.5 lm in diameter containing

haemoglobin

(Hb),

which

comprises

about

a

third of the cell mass. This shape provides a large

surface area for oxygen diffusion into the cell.

The erythrocytes are derived from the same

common pluripotent stem cells as all the other

formed elements of the blood (see Chapter 2,

Figure 2.1) and ultimately from lineage-specific

bone

marrow

cells

under

the

influence

of

cytokines (primarily interleukins and granulo-

cyte-macrophage colony stimulating factor, GM-

CSF) and, finally, erythropoietin (EPO). The latter

is a hormone produced in peritubular kidney cells, and to a lesser extent in the liver, in

response to anaemia and reduced tissue oxygen

levels that together stimulate erythroid precur-

sorsto

divideandmature.Thismechanism

balances RBC production precisely to their loss

through haemorrhage and senescence, etc.

Chronic renal disease (see Chapter 14), many

other chronic diseases and haemodialysis cause

EPO deficiency, which are treated with recombi-

nanthuman

epoetin (EPO).However,some

patients develop antibodies to this and repeated

twice- or thrice-weekly IV or SC injections are

required (SC injections are contra-indicated in

chronic renal failure). Many epoetin analogues

and mimetics are being explored with a view to

minimizing these problems (see References and

further reading).

Maturation

into

erythroid

colony-forming units (CFU-E)

is

promoted

by

an

erythroid colony-stimulating

factor

(CSF-E).

As

the

cells mature in the bone marrow they become increas-

ingly sensitive to EPO and there is progressive loss of ribosomal RNA and mitochondria and increased synthesis of cytoplasmic Hb. In parallel with this, the nucleus becomes condensed and is finally lost, forming reticulocytes.

Reticulocytes are released into the circulation

after about 1-2 days in the bone marrow: nucle-

ated RBCs are not normally present in blood.

Reticulocytes normally retain some ribosomal

RNA and continue to synthesize Hb for a further

1-2 days in the circulation, during which time

the RNA and mitochondria are lost completely

and the mature, enucleate erythrocyte is formed.

The process of erythpoiesis is summarized in

Figure 2.1 (p. 27). The reticulocytes normally

form about 1% of the total erythrocytes, but this

proportion is increased if there is loss of red cells,

e.g. due to traumatic bleeding or haemolysis,

because increased numbers of reticulocytes are

released into the blood as a normal response, to

recover oxygen-carrying capacity.

Because

the

mature

erythrocyte

does

not

contain any DNA or RNA it is not a true cell

and has often been described as a ‘corpuscle’.

However, it has a well-defined, stable structure

and its description as a ‘red blood cell’ is uni-

versally

used.

Erythrocytes

have

a

strong,

deformable cytoskeleton that enables them to

pass through the smallest blood vessels without

damage. The cytoskeleton is composed of sev-

eral interlinked proteins, i.e. alpha- and beta-

spectrins, actin, ankyrin and proteins 4.1, 4.2

and 4.9. The latter proteins are identified by

numbers corresponding to their relative positions on electrophoresis.

About 0.8% (100%/120) of the original cell

population is lost per day and this is normally

balanced by a reticulocyte gain. If erythropoiesis

fails completely, e.g. in aplastic anaemia (Table

11.6), the red cell and reticulocyte counts decline by about 6% per week, with no compensatory reticulocyte gain. Successful treatment in this situation increases the proportion of reticulo-

cytes to above normal levels in the short term, until normal function is achieved.

Although RBCs lose their ability to synthesize

protein

and

carry

out

oxidative

metabolism

they

retain

some

crucial

metabolic

capacity.

This includes the anaerobic Embden-Meyerhof

glycolytic

pathway,

which

provides

four

functions:

•

Production of energy via ATP.

•Maintenance of the red cell membrane and

cell architecture.

•

Formation of NADH to maintain the iron of

haem in the ferrous state.

•Production

of2,3-diphosphoglycerate(2,3-

DPG) that modulates Hb function (see below).

Thereis

alsoahexosemonophosphate

shunt, which provides NADPH to preserve the

sulphydryl groups of HbA and so maintain Hb

tertiary structure. This metabolism is essential to

protect the cells from oxidative stress and yield

the

normal

erythrocyte

life

span

of

about

120 days. These pathways are outlined in Figure

11.1.

The survival of RBCs and the sites of destruc-

tion of senescent RBCs, primarily the liver and

the spleen, can be determined by radiolabelling

with 51Cr and monitoring the change in radia-

tion levels with time and the sites of concentra-

tion of radiation, measured with an external

gamma-camera.

Table 11.1 lists normal values for some haema-

tological and biochemical parameters.

Haemoglobin synthesis and function

Haemoglobin (deoxygenated haemoglobin, Hb)

is the component of the erythrocyte that trans-

ports oxygen from the lungs to the tissues and

some carbon dioxide from the tissues to the

lungs. Hb is produced in the mitochondria of the

developing red cells. In adults, most of it is HbA,

an allosteric protein composed of two alpha

polypeptide chains and two beta polypeptide

chains, i.e. a2b2, the remainder comprising about

3% of HbA2

(a2d2) plus HbF (fetal Hb). HbF is

slightly different from the adult form, being a2c2,

which binds oxygen more strongly than HbA.

Eachglobin

moleculebindsonemoleculeof

the iron-porphyrin haem, so the complete Hb

molecule contains four molecules of haem.

Also present in the red cell is 2,3-diphospho-

glycerate (2,3-DPG), formed by red cell glycolysis

(Figure 11.1), which binds the beta chains and

stabilizes the Hb in a tense conformation that

has a lower affinity for oxygen than the relaxed

conformation produced when Hb binds oxygen

to form oxyhaemoglobin (HbO2). This has impli-

cations for Hb function. The 2,3-DPG is formed

in the RBCs mostly under the relatively anaer-

obic conditions in the tissues and its binding

promotes the release of oxygen there. In the

aerobic conditions in the lungs less 2,3-DPG is

produced, thus favouring the relaxed conforma-

tion that promotes oxygen uptake to form HbO2.

The differing pH and carbon dioxide concentra-

tions between the lungs and the tissues reinforce

these reactions, thus favouring oxygen uptake by

Hb in the lungs and HbO2 dissociation to release

oxygen in the tissues.

Under normal conditions about 98.5% of the

oxygen is transported as HbO2 and the remainder

is dissolved in the plasma. Carbon dioxide, being

very soluble, is carried mostly (70%) as bicar-

bonate in the plasma, 23% is combined with Hb

as carbaminohaemoglobin (HbCO2) and about

7%

is

carried

dissolved

in

plasma

which,

in

equilibrium with the bicarbonate, forms a pH

buffering system.

The Hb from effete red cells is broken down into iron, porphyrins and amino acids, which

are recycled.

Iron metabolism

The dietary iron intake is matched very closely

to iron losses. There is no specific mechanism

for transport into the gut and iron lost in this

way, e.g. by shedding of enterocytes, is highly

conserved. The normal average daily diet in the

UK

contains

about 15-30 mg

of

ferric

iron,

mostly

from

iron-fortified

breakfast

cereals,

less

than 10%

of

which

is

absorbed

in

the

duodenum and jejunum. The factors affecting

iron absorption are listed in Table 11.2.

Before this iron can be absorbed it must be

reduced to the ferrous state. Specialized cells in

the mucosal crypts of the gut migrate to the

luminal

surface,

where

they

produce

a

ferri-

reductaseand

adivalentmetaltransporter

(DMT1)

in

the

villi

of

the

enterocyte

brush

border. The DMT1 then carries the ferrous iron

across the cell membrane by an active transport

lood cell production and function709

process.

Iron is

stored

in

the

cells

as

ferritin or

transferred

into

the

plasma

by

another

transporter via the enterocyte base.

Three control mechanisms are involved. After an iron-rich meal a dietary regulator makes the villi resistant to further iron absorption for some days. The ‘memory’ of the iron status of the

body at the time of their formation then regu-

lates iron transport into the enterocytes. Finally, there

is

a

means

of

signalling

the

level

of erythropoiesis to the enterocytes. Further iron is lost from ferritin stores in the enterocytes when these are shed into the gut lumen.

There is also some dietary haem iron from

animal meat, and some from Hb breakdown,

which is more readily absorbed than elemental

iron.

Iron transport and storage

Most of the total body iron is transported in the

plasma

as

Hb.

However,

the

serum

contains

about 11-30 lmol/L, bound to the specific trans-

porter transferrin, which is synthesized in the

liver: the higher levels occurring in the morning.

Each molecule of transferrin binds two atoms of

ferric iron derived mostly from RBC breakdown

in reticuloendothelial macrophages and oxidized

in arterial blood. The iron-transferrin complex

binds to specific receptors on erythroblasts and

reticulocytes in the bone marrow, where the iron is released and recycled into haem.

About a third of the total iron load is stored in

the

hepatocytes,

reticuloendothelial

cells

and

skeletal muscle, mostly as ferritin and normally

about a third as haemosiderin. The latter is an

insoluble protein-iron complex found in the

liver, spleen and bone marrow, where it can be

visualized by light microscopy after staining,

unlike ferritin.

Persistenceof

haemosiderinin erythroblast

mitochondria occurs in sideroblastic anaemia

(see below), which may be inherited or acquired

(Table 11.2).

It

is

due

to

a

failure

of

haem

synthesis,which

mayreflectpoisoningof

enzymes by drugs, e.g. isoniazid, or toxins, e.g.

alcohol or lead.

Useful indicators of iron status include serum

iron, ferritin level and total iron-binding capacity

(TIBC).

Anaemia

The unqualified use of the term ‘anaemia’ means

simply that the level of functional Hb in the

blood falls below the reference level appropriate

to the sex and age of an individual. The WHO

defines these lower levels arbitrarily as 13 g/dL in

adult males (normal range (N)

13-17) and

12 g/dL in adult females (N

12-16). Children

of both sexes below 14 years of age have lower

levels, the cut-off for anaemia being 11 g/dL in

those aged 6 months to 6 years and 12 g/dL in

the 6-14

age

group.

Levels

are

normally

measured at sea level. These values may differ

between populations and at altitudes where the

partialpressure

ofoxygenislow,causing

increased

RBC

and

Hb

production.

However,

many apparently normal individuals have Hb

levels below these arbitrary values.

Defined in this way anaemia is the common

outcome of many different pathologies, i.e. it is

a secondary condition, and it is important to

diagnose the underlying cause, so that specific

treatment can be given. Thus some forms of

anaemia have an adjectival prefix that describes

the underlying disorder, e.g. pernicious anaemia,

aplastic

anaemia (p. 725),

leucoerythroblastic

anaemia, due to space-occupying lesions of the bone marrow, e.g. leukaemia.

Anaemia is a very common blood disorder and is believed to affect about 30 million people

worldwidebut

thetrue figureisunknown

because of poor data from deprived areas with poor nutrition and unknown levels of intestinal parasites causing blood loss.

Itis

convenienttodiscussanaemiaunder three headings:

•

Normocytic, normochromic. •

Microcytic, hypochromic. •

Macrocytic.

Investigation of anaemia

It is not possible to diagnose anaemia by observa-

tion, e.g. by unusual pallor of complexion or of the inner surface of the lower eyelid. However, if there are other symptoms or signs that may be explicable by anaemia these features may prompt investigation. Anaemic patients often complain of non-specific conditions (tiredness, reduced exer-

cise tolerance and shortness of breath), but these are more usually due to very common condi-

tions (being overweight, inadequate exercise and unfitness, depression, and CVD).

The results of simple laboratory tests, obtained with automated blood cell counters, which give rapid results, include:

•Mean cell volume (MCV, in femtolitres [fL]).

•

RBC distribution width (RDW), a measure of

the variability of MCV.

•

Mean corpuscular Hb (MCH, in picograms/

RBC [pg]).

•

Mean cell Hb concentration (MCHC, in g/dL).

Secondary parameters derived from these, e.g.

the MCV/MCH ratio, are also used. However, the

microscopic examination of a stained blood film

permits an examination of red cell morphology

which, considered with other laboratory and

patient data, usually gives the diagnosis. Even if

these data are not conclusive they will guide

further

testing

for

specific

conditions,

e.g.

microscopy of bone marrow to investigate cell

morphology or after a trephine with a special

largeneedle

toobtainasampleofboneto observe bone marrow architecture and the pres-

ence of abnormal cells. These samples are usually

obtainedfrom

theposterioriliaccrest.The

trephine biopsy has to be processed as a tissue

sample,so

theresultisavailableonlyafter

several days.

Normocytic, normochromic anaemias

One group in this category, i.e. those with a

normal or low reticulocyte count and normal

bone marrow morphology, are often described as

secondary anaemias, because there is always an

Anaemia

711

underlying condition(Figure

11.2). Diagnosis then depends on tests to identify the latter and exclude serious pathology, e.g.

•

Bleeding, destruction of RBCs (haemolysis),

especially in the acute stage.

•

Leukaemias and bone metastases (secondary

deposits) from primary cancers elsewhere in

the body (see Chapter 10).

•Aplastic

anaemiasorabnormalcell

production.

•

Renal failure, causing failure of erythropoietin

production.

•The early stages of the anaemia of chronic

disease (see below).

Haemolytic anaemias

The

body

can

respond

up

to

eightfold

by

increasing RBC production and by increasing the

amount of active marrow. Provided the rate of

loss is less than the capacity of the marrow to

respond, higher than normal RBC destruction

does not always cause anaemia. However, the

proportion

of

reticulocytes

is

increased,

and

there may be spherical or other abnormally-

shaped RBCs or red cell fragments. The many possible

causes

of

haemolytic

anaemia (see below) are listed in Table 11.3.

Extravascular haemolysis

Most

haemolytic

anaemias

result

from

RBC

breakdown by reticuloendothelial macrophages,

notably in the spleen, i.e. extravascular haemol-

ysis. These are often the result of inherited RBC membrane defects.

Inhereditary

spherocytosis(HS)the RBC

membrane is weakened and poorly supported by

the cytoskeleton, resulting in somewhat spher-

ical cells that are more rigid than the normal

biconcave

disks.

The

abnormal

cells

cannot

negotiate the small vessels of the spleen and are

broken down there. The inheritance is usually

autosomal-dominant and affects about 1/5000

northern Europeans, though it may skip a gener-

ation, but may be due to a recessive pattern of

inheritance, or new random mutations in some

cases.

There is a wide variation in the age at presen-

tation, some babies being jaundiced at birth

whereas others may be hardly affected. Chronic

haemolysis

causes

pigment

gallstones

(see

Chapter 3), splenomegaly, and folate deficiency.

Affected

neonates

require

repeated

blood

transfusions

until

they

are

old

enough

for

splenectomy, which is usually curative. However,

splenectomy carries a life-long risk of serious

infection so is indicated only if justified by the

severityof

thepatient’scondition.Multiple

immunizations and antibiotic prophylaxis are

required.

Hereditary

elliptocytosis

is

about

twice

as

prevalentas

HSandissomewhatsimilar,

though milder. Less than 10% have significant

haemolysisand

splenectomyisrequiredonly

occasionally.

Intravascular haemolysis

In all haemolytic anaemias the RBC survival is reduced, but the survival time is determined

only rarely.

Destruction

of

RBCs

within

the

circulation

releases Hb. Some of this is bound by plasma

protein,

but

excess

is

filtered

at

the

renal

glomeruli and most appears in the urine, though

some is reabsorbed by the tubular cells in which it

isdeposited

ashaemosiderinandcanbe

detected in the urine. Part of the plasma Hb is

oxidizedto

methaemoglobin,whichcannot

function as an oxygen carrier and breaks down

to globin and ferrihaem. The latter is usually

bound in the plasma, but excess binds to albumin

as methaemalbumin, which can be detected in

Anaemia

713

the plasma photometrically: this is the basis of

the Schumm test. All of the HbA and its products

are metabolized in the liver and recycled into Hb.

The consequences of intravascular haemolysis include:

•

High

serum

unconjugated

bilirubin,

high

urinary urobilinogen and raised serum lactic

dehydrogenase, which are indicators of RBC breakdown.

•

Indicators

of

increased

erythropoiesis,

e.g.

increased proportion of reticulocytes.

In some haemolytic anaemias there may also be abnormally-shaped RBCs or red cell fragments (see below).

Abnormal red cell metabolism

The RBC has very restricted metabolic capacity,

the

principal

systems

being

the

Embden-

Meyerhof pathway and the connected hexose

monophosphate shunt (see Figure 11.1). There

are

two

main

enzyme

deficiencies

that

may

occur, one each in each of these pathways.

Glucose-6-phosphate

dehydrogenase

(G6PD)

deficiency.

This is the most common of the

enzyme

deficiencies.

There

are

numerous

isoforms of the enzyme, the genes for which are

X-linked. Heterozygous females may have two

different populations of RBCs and may appear to

be clinically normal but all females homozygous

forthe

mutantareaffected.Theenzymeis

involved

in

the

production

of

NADPH (see

above) and is crucial for the maintenance of

glutathione, and so the flexibility and integrity

of the RBC. Its absence causes RBC rigidity and

leakage and the oxidation of Hb to methaemo-

globin, which is deposited on the inner surface

of the membrane. The result is haemolysis in the

spleen. Over 100 mutant forms are known.

G6PD deficiency involves millions of people in central Africa, the Mediterranean borders, the Middle East and South-East Asia. In some areas up to 40% of the population may be affected,

especially males.

The reduction of enzyme activity renders the

RBCs very sensitive to oxidative stress. There

may be:

•

Neonatal jaundice.

•

Chonic haemolytic anaemia.

•Acute haemolytic episodes due to:

-

Drugs (Table 11.4).

-

Bacterial and viral infections and diabetic

ketoacidosis.

-Ingestion of fava beans.

Diagnosis may be difficult because the RBC

count is normal between attacks. However, there

will be evidence of haemolysis, especially during

attacks, though this may be self-limiting because

the older, more affected RBCs are damaged selec-

tively. Many RBCs will have irregular margins,

with ‘bites’ taken out of the membrane where

deposited methaemoglobin has been removed in

the spleen. Direct assays for G6PD are available.

Treatment involves avoidance of any causative

drugs, treatment of infections (see Chapter 8)

and proper management of diabetes mellitus (see

Chapter 9). Blood transfusions are often essential

and splenectomy may help, but this is unlikely.

Pyruvate kinase (PK) deficiency is the second

most common of the enzyme deficiencies, but

much less so than G6PD. It causes low levels of

ATP and increased levels of 2,3-DPG (see Figure

11.1),

and

so

energy-starved

and

rigid

RBCs.

The high levels of 2,3-DPG (see above) minimize

the severity of anaemia, by increasing oxygen

unloading in the tissues. The blood film shows

‘prickle

cells’

and

reticulocytosis.

The

most

prominent

signs

are

anaemia,

jaundice

and

splenomegaly. Exchange blood transfusions are

required in infancy, pregnancy and infections,

throughout life. Aplastic crises may occur. In

severe cases, there may be bone changes similar

to those seen in thalassaemia (see below).

Splenectomy may be helpful and may reduce

the need for frequent blood transfusions. Folic

acid supplementation is needed (see Figure 11.4).

Abnormal

Hb

synthesis.

These

conditions

may cause abnormal globin chain production

(thalassaemias)

or

abnormal

globin

chain conformation (sickle-cell anaemia).

Thalassaemias occur in a wide arc, stretching from Spain to Indonesia but may occur in any population. The name comes from the Greek

word for sea: all the countries with affected

populations have extensive sea borders. They are the result of differing relative rates of production of the alpha and beta chains, or a complete

absence of one of these.

Beta-thalassaemias are caused by a complete

or relative absence of beta-globin chains, and

affect

all

races.

The

excess

of

alpha-chains

combines with gamma and delta Hb chains,

producing very low levels of normal HbA and

increased levels of HbA2

and HbF (see above).

Mutations in the beta-globin gene cause the

production of unusable forms of Hb. Alpha-

thalassaemias mostly affect Orientals and those

of Middle Eastern origin. Thalassaemia minor

(thalassaemia trait) is an asymptomatic or mildly

symptomatic heterozygous state. Thalassaemia

major is the result of beta-chain gene mutations

giving a homozygous state, or doubly heterozy-

gous state, i.e. the H6 genes from each parent are

mutated

in

different

ways.

There

is

severe

anaemia

from

the

age

of

3-6 months,

when

there is normally a switch from the gamma-

chain production characteristic of fetal Hb (HbF,

a2c2), to beta-chain production, characteristic of

normal adult Hb (a2b2). However, HbF synthesis

continues beyond this point and most patients

have

some

HbF.

The

liver

and

spleen

are

enlarged, sometimes grossly, and the erythropoi-

etic

bone

marrow

extends

abnormally

into

bones that are not normally haemopoietic, e.g.

in the face and hand, causing facial, and some-

times hand, deformities. The anaemia is severe

and regular blood transfusions are required, but

if these are needed frequently splenectomy is

indicated (see above).

Frequent transfusions lead to haemosiderosis,

i.e. iron overload from deposition of haemosiderin

in tissues, causing widespread organ damage if it

is not corrected. This requires removal by vene-

section (i.e. regular bleeding), provided that the

patient has a functional bone marrow to replace

the leucocytes that are lost. Regular folic acid

supplementation

and

ascorbic

acid

are

also

required. The latter enhances iron excretion by

Anaemia

715

keeping the excess iron in the more soluble

ferrous state.

Complexing with desferrioxamine mesilate, an

ironchelating

agentthatbindstissuestores

rather than Hb iron, is an alternative to venesec-

tion. It is given as an overnight SC infusion, or

by syringe driver, 3-7 times a week according

to need. Desferrioxamine may also be given at

the same time as a blood transfusion, but must

not be mixed with the blood or given via the

same infusion line: administration via the same

cannula when the transfusion is complete is

convenient. Iron excretion is again enhanced by

giving ascorbic acid.

Deferiprone

is

a

newer,

orally

active

iron-

chelatingagent

foruseifdesferrioxamineis

contra-indicated or is not tolerated. However,

fertile women should take strict contraceptive

precautions

because

deferiprone

is

a

known

teratogen and is embryotoxic. Blood dyscrasias,

notably agranulocytosis, have also been reported,

so weekly neutrophil counts must be done and

patients and their carers warned to report imme-

diately any signs of infection, e.g. fever or sore

throat. Filgrastim may be required (see Chapter

10). Care is required if there is any renal or

hepatic impairment.

Deferiprone also complexes zinc, so plasma zinc concentrations also need to be monitored. Joint pain may occur.

As usual with complex medications the manu-

facturers’ literature should be consulted on the use of both of these agents.

Alpha-thalassaemias

have

a

more

complex

inheritance

because

alpha-chain

synthesis

is

controlled

by

two

pairs

of

structural

genes,

onepair

fromeachparent.Becausethereare

four

alpha

genes,

there

are

four

possible

conditions:

•

Single gene deletion confers the carrier state,

and subjects are haematologically normal.

•

Deletion of two genes causes a mild hypo-

chromic microcytic anaemia (see below), i.e. thalassaemia trait.

•

Deletion

of

three

genes

results

in

HbH

disease. There is a variable degree of anaemia,

splenomegaly and the RBCs are typical of

thalassaemia (see above).

•

Deletion of all four genes is incompatible

with life and babies are stillborn with features

similar to those of severe beta-thalassaemia.

Women at risk who wish to bear a child are

identified on the basis of racial and geographical

origin and personal or family history and are

usually offered antenatal diagnosis. If they carry a

genetic abnormality, and their partner also carries

thalassaemia

genes,

the

mother

is

normally

referred for fetal genetic diagnosis, and offered

termination

of

the

pregnancy

if

the

fetus

is

severely affected.

Sickle-cell syndromes

These inherited Hb defects affect people mostly

in central Africa (25% population carriage of the

defective gene) and parts of the Middle East and

India. Afro-Caribbeans are commonly affected.

There is often co-inheritance of the sickle cell

gene with those for beta-thalassaemia and other

abnormal Hb conditions. The condition may be

homozygous, giving HbSS and causing sickle-

cell anaemia, or heterozygous (HbAS), causing

sickle-cell trait.

The deoxygenated HbS is insoluble, and poly-

merizes in the RBC. This is initially reversible, but the cells finally take on their characteristic, rigid sickle shape. These cannot negotiate the microcirculation and there is clotting and tissue infarction,

often

in

the

bones.

Because

HbS releases its oxygen more readily than normal Hb, patients usually feel well, but a sickling crisis may be triggered by hypoxia.

The heterozygous condition (HbAS) is initially

mild, because infants produce fetal Hb (HbF) for

3-6 months. Symptoms then become apparent,

due to a change from producing HbF to HbS, in

place of the normal HbA. High levels of HbF

tend

to

prevent

sickling

and

many

Middle

Eastern

and

Asian

people

co-inherit

increased

HbF

levels

and

have

relatively

mild

disease

becausefetal

Hbisamoreefficientoxygen

carrier than HbA.

Complications are the result of anaemia and

circulatory impairment. Although patients are

often generally well, they suffer chronic anaemia

and repeated painful sickling crises, caused by a

variety of stressors, e.g. infection, dehydration,

acidosis,

exposure

to

cold

and

anaesthetics.

Crises cause severe pain and opioid analgesics

(see Chapter 7) may be required. Special care is needed if anaesthesia is contemplated.

Renal

impairment

is

common

in

late

stage

disease and may progress to renal failure. Infec-

tions,

especially

pneumococcal

disease,

are

common and need immunization and prophy-

lactic antibiotics. Aseptic bone necrosis, Salmo-

nella

osteomyelitis

and

chronic

leg

ulceration

occur. Pulmonary hypertension occurs, due to

RBC sequestration in the lungs and ischaemic

liver cirrhosis, and a severe pulmonary syndrome

may occur. Excess bilirubin production causes

pigment gallstones (see Chapter 3). Strokes are

relatively common.

Between crises, patients require regular folic

acid and prompt treatment of infections. Crises

that cannot be managed with analgesics require

hospital admission. Blood transfusion is required

only if their Hb level falls significantly below

their norm. Transfusion also aborts a sickling

crisis if the proportion of sickle cells is reduced to

less than about 30%. Exchange tranfusion, i.e.

withdrawal of the same volume of the patient’s

blood as is transfused, may be required to avoid

excessive

blood

viscosity

and

so

reduced

microvascular blood flow, especially in severe

pulmonary involvement.

Autoimmune

haemolytic

anaemias

are described on p. 723.

Microcytic, hypochromic anaemias

The RBCs have a MCV of

78 fL due to some

disturbance of iron metabolism, and there is a

low MCV/MCH ratio. Following this observa-

tion,examination

ofthebloodfilmusually

permits rapid diagnosis. Figure 11.3 presents an

algorithm for the investigation and diagnosis of

this condition.

There may be:

•

Iron deficiency.

•

Impaired availability of iron, in the anaemia

of chronic disease.

•Defective

globinchainsynthesisin

thalassaemias.

•

Defective

haem

synthesis

in

sideroblastic

anaemia.

Indicators of iron status in anaemias are shown in Table 11.5.

Iron deficiency anaemia

It will be seen from Table 11.5 that the ferritin

level

distinguishes

between

simple

iron

defi-

ciency

and

the

anaemia

of

chronic

disease.

Ferritin is a soluble form of storage iron that is a

good index of total body iron level. Examination

of

a

stained

blood

marrow

film

is

conclusive

if

there

is

any

doubt.

Determination

of

the

percentage of transferrin saturation may also be

useful.

Anaemia

of

chronic

disease.

A

low-grade

anaemia is common in chronic inflammatory

states, e.g. RA and the connective tissue diseases (see Chapter 12), chronic infections, e.g. tuber-

cular osteomyelitis and some fungal infections, and thalassaemia trait (see above).

Sideroblastic

anaemia

is

due

to

abnormal

bone marrow stem cells and may be inherited.

Because it is X-linked, it is transmitted through

the female line. There is defective haem synthesis

and characteristic cells in the bone marrow show

a ring of iron deposits (ring sideroblasts). The

acquired form may be caused by toxins, including

drugs,

e.g.

alcohol

abuse,

isoniazid

and

lead

toxicity. The anaemia may be severe and refrac-

tory to treatment. There is usually a bimodal

distribution of RBC size, with both microcytic

and mildly macrocytic cells. Patients with gener-

ally

poor

production

of

all

cell

types

(pancy-

topenia) have a poor prognosis and may progress

to acute myeloblastic leukaemia (AML).

The thalassaemias are described above.

Macrocytic anaemias

Classification, aetiology and diagnosis

There are megaloblastic, non-megaloblastic and haemolytic types.

Megaloblastic

macrocytic

anaemias

result

from impaired DNA synthesis and nuclear matu-

ration.

RNA

and

protein

synthesis

continues

after nuclear development has ceased, causing a

relatively large immature RBC with a high cyto-

plasmic mass (megaloblasts). Megaloblasts can

be observed in bone marrow smears as unusually

large RBC progenitor cells with dispersed nuclear

chromatin

and

several

nucleoli.

Because

the

factors

causing

defective

erythropoiesis

also

affect all other bone marrow cell lines, thrombo-

cytopenia and leucopenia also occur, usually in

the later stages. Characteristic large leucocytes

may also occur.

Non-megaloblasticmacrocytic

anaemiasare

usually due to toxic agents, non-bone marrow

organ failure, e.g. alcoholic liver disease and hypothyroidism,or

aplasticanaemias(bone marrowfailure;seebelow). RBCagglutina-

tion

produces

large

clumps

of

cells

that

may be

reported

erroneously

as

macrocytosis

by automated blood analysers.

Megaloblastic

macrocytic

anaemias

may

be due to:

•

Deficiency

of

vitamin

B12

or

folic

acid

(Table11.6 and Figure 11.4), or abnormal

metabolism of these.

•Therapy

withdrugsinterferingwithDNA

synthesis, e.g. azathioprine, cytarabine, cyclo-

phosphamide,

fluorouracil,

hydroxycarbmide,

mercaptopurine,

tioguanine

and

zidovudine.

Aciclovirand

ganciclovirmayalsocause megaloblastosis.

•

Deficiency

of

enzymes

essential

for

DNA

synthesis.

Diagnosis and aetiology

A

scheme

for

the

diagnosis

of

macrocytic anaemia is given in Figure 11.5.

Because reticulocytes are larger than normal

RBCs, any situation causing significant blood

loss, e.g. trauma or haemolysis, will result in the

release of reticulocytes from the bone marrow,

causing a reticulocytosis and macrocytosis, at least in the short term, until treatment corrects the abnormalities.

Deficiencies of vitamin B12

or folic acid are

usually

of

dietary

origin,

e.g.

strict

vegans,

malnutrition,gastrointestinal

problems (e.g.

malabsorption, see Chapter 3), excessive alcohol

intake,medication

history,gastriccarcinoma

and

gastrointestinal

surgery.

These

potential

causes need to be investigated. Hypothyroidism

may be associated with pernicious anaemia and

smoking may also cause vitamin B12 deficiency.

Folate

deficiency

occurs

in

malabsorption,

pregnancy, neoplastic diseases associated with a

high cell turnover, including severe infections.

Antifolate

medication,

e.g.

methotrexate

and

trimethoprim, anticonvulsants, e.g. phenobarbital,

phenytoin

and

primidone,

causing

increased

demand, and loss of folic acid in peritoneal dial-

ysis and haemodialysis (see Chapter 14) may also

contribute to low blood folate levels. An acute

onset may occur in those with marginal folate

stores.

Heavy menstrual losses in women and haemo-

lytic anaemias (see above) also cause deficiencies.

Clearly, assays for vitamin B12and tests to

establish the reasons for low levels are required, e.g.

absorption

tests (Schilling

test

and

anti-

bodies

to

parietal

cells,

intrinsic

factor

and thyroid tissue), and establishment of the origin of folate deficiency are required.

Macrocytosis occurring with a normal RDW usually

indicates

heavy

alcohol

consumption and this is confirmed by a high serum level of gamma-glutamyl transpeptidase (GGT), a marker of liver damage.

Management of anaemias

This must be based on specific therapy and thus

depends on accurate diagnosis. Effective treat-

ment

should

give

an

increased

reticulocyte

count within 10 days. If this response does not

occur, or if the Hb level does not improve, the

diagnosis should be reviewed. Clearly, if anaemia

is due to an underlying disease state, e.g. the

anaemia

of

chronic

disease,

treatment

must

involve

correction

of

that

condition,

in

addi-

tion to the application of appropriate specific

therapy.

Blood transfusion may be indicated if there

has been a sudden fall in the erythrocyte count

orHb

concentration,e.g.inacutedrug-or

infection-induced

haemolytic

crises

in

G6PD

and pyruvate kinase deficiency (see Figure 11.1

and pp. 713 and 714) and inherited RBC disor-

ders. It is also the mainstay of treatment in

thalassaemias

and

in

sickle-cell

disease (see

above).Transfusion

ishazardousinelderly

patients

because

the

rapid

increase

in

blood

volume

raises

the

blood

pressure

and

this,

together with the associated increase in venous

return stresses the heart. Both of these are unde-

sirable in those with compromised cardiac func-

Anaemia721

tion (see Chapter 4). Cardiac stress is also caused

if the recipient’s cell count is near normal, due to

increased blood viscosity. Further, the procedure

carries the risks of infection and immunological

errors, despite rigorous protocols. Repeated tran-

fusionsof

wholebloodcausetransfusion

haemosiderosis (iron

overload),

with

liver,

pancreas,

heart

muscle

and

endocrine

gland

damage. This usually requires treatment with the

iron-chelating agent desferrioxamine (see above).

The alternative, orally active chelating agent

deferiprone is licensed for use in patients with

thalassaemia major (see above) in whom desfer-

rioxamine is contra-indicated, or are intolerant

of

it.

However,

it

may

cause

serious

blood

dyscrasias.

Erythropoietin

Darbepoetin and erythropoietin alfa and beta are

useful only in the anaemia of chronic disease,

especially renal disease, notably those on dialysis

(see Chapter 14), and in those receiving cancer

chemotherapy (see Chapter 10). They are also

used in patients with moderate anaemia, i.e. Hb

10-13 g/dL,

who

are

awaiting

major

surgery

likely

to

involve

major

blood

loss,

e.g.

hip

replacement, to minimize the need for blood

transfusion.

Iron therapy

Iron deficiency is often difficult to treat. The

preferred treatment is to use ferrous sulphate

tablets (1 tablet

65 mg Fe2

), one before break-

fast, because it is better absorbed on an empty

stomach. Further, diets that include bran, muesli

or wholemeal bread contain phytates, which may

interfere with iron absorption. Twice-daily dosing

may be needed if there is continuing blood loss,

but the commonly prescribed three times daily

regimen is usually excessive and is needed only

rarely. However, iron may cause gastrointestinal

side-effects (see below) that cause patient non-

adherence, so after-meal dosing may have to be

accepted.

Ferrous fumarate may be a suitable alternative if a patient is intolerant of ferrous sulphate and the 200-mg tablet provides the same amount of iron as a ferrous sulphate

tablet. There are several liquid dosage forms that are suitable for infants and young children.

Treatment is continued for 2-4 months after the Hb level has been normalized, to replenish iron stores.

Injections

of

iron

dextran

or

iron

sucrose

are

rarely required, but may be needed if a patient

is intolerant of oral iron, and if there is malab-

sorption (see Chapter 3) or continuing bleeding.

There is no good evidence to support the use of

slow-release

or

compound

oral

products. Although they are less likely to cause gastro-

intestinal upset, this is possibly because only a small proportion of the dose is absorbed.

Iron and folic acid tablets are given prophy-

lactically

to

pregnant

women

at

risk

of

the

combined deficiency. However, the amount of

folic acid in these is too low for the prevention

of neural tube defects in the fetus (see below)

and for the treatment of megaloblastic anaemia.

Tolerability is the determining factor in the

choice of product. Nausea and epigastric pain

are common and are dose-related, but this does

not seem to hold for diarrhoea or constipation,

though

dose

reduction

may

help.

Ferrous

gluconatetablets

containing 35 mgFe2,i.e.

about

half

the

amount

in

ferrous

sulphate

tablets, or one of the liquid preparations, will be

needed for this. Oral iron may exacerbate diar-

rhoea in patients with IBD (see Chapter 3) and

this

occurs

more

commonly

with

modified-

release forms that are released lower in the GIT.

Also,

care

must

be

exercised

in

those

with

bowelstricture (narrowing)

anddiverticular

disease (see

Chapter

3).

Constipation

is

espe-

cially likely in older patients and may lead to

faecal impaction.

Correction of vitamin B12 and folate deficiencies

Vitamin

B12

deficiency.

Hydroxocobalamin

is

given intramuscularly, 1 mg on alternate days for

5-6 doses

to

replenish

normal

body

stores,

mainly in the liver, of 3-5 mg. An alternative

regimen is to give the 1-mg dose on 3 days a week

for 2-3 weeks. Because daily losses are normally

very small, this is sufficient to maintain require-

mentsfor

2-4 years’normalmetabolism.Due

to the long persistence of hydroxocobalamin, a

maintenance dose of 1 mg is then given every

2-3 months, usually for life. Clinical improve-

ment is rapid ( 48 h) and a maximal reticulocyte

response

occurs

in

about

7 days.

However,

existing long-standing CNS damage, a result of vitamin B12 deficiency, is irreversible.

Cyanocobalamin is no longer used because it

is excreted more rapidly than hydroxocobalamin

and

requires

monthly

injections.

It

is

now

known that giving a 2-mg dose PO daily is also

effective,

but

only

50-lg

tablets

are

available.

Theuse

oflow-doseoralpreparationsasa

‘tonic’ is irrational. However, they are prescrib-

able under the UK NHS for vegans and others

with a dietary deficiency, both for prevention

and

treatment

of

vitamin

B12

deficiency,

though

this

is

inferior

to

hydroxocobalamin

treatment.

Isolated

folate

deficiency

should

not

be

correctedunless

vitaminB12 levelsare

adequate,

because

the

latter

is

essential

for

correct

folate

metabolism

and

giving

folate

makes

extra

demands

for

vitamin

B12 (see

Figure 11.5). This may produce frank vitamin

B12

deficiency

in

a

patient

with

a

marginal vitamin B12

level and so may cause widespread neurological damage. For this reason, multivit-

amin products, e.g. vitamins capsules, do not

contain folic acid. Low levels of vitamin B12 also prevent full folate metabolism, so the folic acid is not available for normal purposes. If folate

needs to be given and the patient’s vitamin B12 status

is

suspect

or

unknown,

both

folic

acid and vitamin B12

should be given.

The normal therapeutic dose is 5 mg of folic

acid

daily,

the

same

as

is

used

in

chronic

haemolytic disease. Women trying to conceive

should take a prophylactic dose of 200-400 lg

daily, or 400-500 lg daily for those at risk of a

first neural tube defect, e.g. if either wife or

husband

has

a

neural

tube

defect.

However,

4-5 mg daily until the 12th week of pregnancy is

needed to prevent a recurrence of a neural tube

defect.

Folic

acid

may

reduce

the

plasma

concen-

trations

of

antiepileptics (see

Chapter 6),

i.e. phenytoin, phenobarbital and primidone.

Acquired haemolytic anaemias

Inherited haemolytic anaemias, including those due to congenital metabolic defects, are discussed on pp. 712-716.

Non-immune haemolytic anaemias

Theseare

onetypeofacquiredhaemolytic

anaemia.

There

are

numerous

non-immune

causes of intravascular haemolysis, for example:

•

Mechanical RBC damage caused by excessive

turbulence or shear in the circulation:

-

Calcified

heart

valve

stenosis

and

mal-

functioning mechanical heart valves (see

Chapter 4).

-Martial arts or prolonged running, which

damage RBCs in the circulation of the feet.

-

Microangiopathic

haemolytic

anaemia,

caused

by

severe

hypertension

(see Chapter 4).

-Infection, e.g. disseminated intravascular

coagulation (see Chapter 2).

-

Inflammatory conditions, e.g. polyarteritis

nodosa (see Chapter 13).

•Paroxysmal

nocturnalhaemoglobinuriais

due to a rare RBC membrane defect causing

extreme

sensitivity

to

complement

C3

(Chapter 2).

As

the

name

implies,

the

haemoglobinuria is increased during sleep.

These

non-immune

causes

of

intravascular

haemolysis are not discussed further in this text.

However, most haemolysis is extravascular and

results from RBC destruction in the phagocytic

cells of the reticuloendothelial system in the

liver, bone marrow and, especially, the spleen. If

the bone marrow is able to respond, so that RBC

replacement is able to keep pace with destruc-

tion, i.e. there is compensated haemolysis; the

condition does not require treatment. Pharma-

cotherapeutic or surgical intervention is appro-

priate only if the condition causes respiratory or

cardiovascular limitation or there is a serious

underlying condition.

Autoimmune haemolytic anaemias

These are due to the production of anti-RBC

autoimmunoglobulins (auto-Igs;

Chapter 2).

They are detected by a positive direct Coomb’s

test (Figure 11.6) and can be divided into two

types. That in which the reaction with the auto-

Igs occurs strongly at body temperature is the

‘warm’ type and is due to IgG autoagglutinins.

Reactions that occur below 37°C (often

30°C)

characterizes the ‘cold’ type and involve IgM

autoagglutinins (Table 11.7; see Chapter 2).

Anaemia723

The distinction is important because it affects

management. The cold type responds poorly to

treatment (see below), and patients with cold-

type disease develop symptoms only in a cold

environment.

Pathology.No primary pathogenic aetiology has been identified for either condition, but

associated diseases are listed in Table 11.7.

Autoagglutinins(IGMs)

thatactivatethe

complement

cascade (see

Chapter 2)

cause

intravascular haemolysis. However, IgGs often do

not activate complement, but cells coated with

IgG autoagglutinins may be either completely

phagocytosed in the spleen or their cytoskeleton

is damaged so that they become spherical (sphe-

rocytes) and continue to circulate until they too

are trapped in the spleen and phagocytosed. Thus

IgG autoagglutinins usually cause extravascular

haemolysis.

Investigation.

Results

with

electronic

analy-

sers usually give spuriously low RBC and Hb levels and a high MCV, all of these being due to RBC agglutination. Results with the cold type usually revert to approximate normality if the sample is warmed.

The

warm

type

gives

nearly

normal results in usual laboratory conditions. However, agglutination

is

best

observed

by

microscopy, which also shows spherocytes.

Anaemia is usually mild,

7.5 g/dL of Hb, but severe haemolysis may occur rarely.

Clinicalfeatures

-warmtypehaemolytic

anaemias.

These are more frequent in middle-

aged women than men, but otherwise can occur

in both sexes at any age. They tend to follow a

relapsing-remitting course, but folate deficiency

and infections may cause severe haemolysis. The

commonest associations are with drugs that act

as haptens (see Chapter 2), e.g. methyldopa and

penicillins, and rheumatic and related diseases

(Table 11.7; see also Chapter 12). Lymphomas,

e.g.

Hodgkin’s

disease

and

non-Hodgkin’s

lymphoma, and chronic lymphocytic leukaemia

(see Chapter 10) are also associated. Autoagglu-

tinins against Rhesus antigens (see Chapter 2)

may be present. The spleen is enlarged propor-

tionately to the severity of the haemolysis and is

palpable below the left rib cage.

Management.

Any underlying disease should be treated and alternatives used to replace any drugs that are implicated, but haemolysis may continue for more than 3 weeks even though the drug is completely eliminated.

Patients should not normally receive blood

transfusions, because autoagglutinins are wide-

spreadin

donorserum,andcarefulcross-

matching at 37°C is required if transfusion is

essential. Washed red cells carry very little donor

serum, but cross-matching of donor RBCs with

the recipient’s serum is essential to avoid lysis of

donor RBCs.

High-doseprednisolone

is effective in about

80% of patients and reduces the production of

autoagglutinins, by suppressing B and T cell

activity. It may also suppress RBC destruction in

the spleen. If there is no response, or if relapse

occurs when the dose is reduced, splenectomy is

required. However, even this may be inadequate

and immunosuppression, e.g. with azathioprine

or cyclophosphamide

(see Chapter 10), is then

required.

Clinical

features

-

cold

type

haemolytic

anaemias.

In about 50% of patients no cause

can be found, especially in the older age group.

This form is usually associated with a gradual

onset

of

chronic

haemolysis.

Infections,

e.g.

infectious

mononucleosis

(‘glandular

fever’,

due to Epstein-Barr virus), Mycoplasma pneumo-

nias,

and

cytomegalovirus

infections

are

the

commonest cause in the remainder, with an

acute

presentation.

This

latter

form

may

be

severe. Acrocyanosis, e.g. Raynaud’s phenom-

enon (see Chapter 12) and similar blanching of

the skin in the feet, occurs in cold conditions.

Management.

Apart from treating any associ-

ated conditions, e.g. infections, and avoidance of cold conditions, little can be done. None of the treatments used for warm type disease, i.e. pred-

nisolone, splenectomy and immunosuppression, is usually effective.

Neutropenia and agranulocytosis

Neutropenia

is

defined

as

a

neutrophil

count

1.5 ÷ 109/L. An almost complete absence of

Neutropenia and agranulocytosis

725

neutrophils

is

agranulocytosis,

because

they form about 85% of the total granulocyte count, i.e. neutrophils, eosinophils and basophils, and the factors that underlie neutropenia also affect other granulocytes.

Aetiology

•

Inherited:

ethnic

(more

common

in

non-

white races), numerous rare inherited defects.

•

Treatment of neoplastic disease with cytotoxic

drugs (see Chapter 10).

•

Following stem cell transplantation.

•

Aplastic anaemia, i.e. bone marrow failure,

which may be:

-

congenital;

-due to drugs or chemicals, e.g. penicillins,

cephalosporins, chloramphenicol, gold salts,

antiepileptics

(phenytoin,

carbamazepine), oral

hypoglycaemic

agents,

NSAIDs, quinine,

volatile

aromatic

hydrocarbons (‘glue sniffing’);

-

result of infections, e.g. Epstein-Barr virus,

hepatitis, HIV/AIDS, TB, typhoid fever;

-

due

to

bone

marrow

infiltration

with

neoplastic

cells,

e.g.

in

leukaemias

and lymphomas.

•

Megaloblastic anaemia (see above).

• RA, Felty’s syndrome, SLE, Sjögren’s syndrome

(see Chapter 12).

Symptoms

These are primarily infections that increase in frequency and severity as the neutrophil count falls. Below 0.5 ÷ 109/L life-threatening pneu-

monia and septicaemia are likely. Chronic tired-

ness may be regarded as a minor condition, thus delaying diagnosis and treatment.

Childrenare

usuallydiagnosedatabout 4-6 months of age, but the course of the disease isfairlybenignandinmostcasesremits

spontaneously after 6-24 months.

Diagnosis

This

depends

on

a

low

neutrophil

count,

examinationof

abonemarrowtrephine, demonstration of antineutrophil antibodies and

the detection of other autoimmune conditions.

Pharmacotherapy

Any implicated drugs should be stopped and

associated conditions treated. Prompt treatment of

infections

with

parenteral

broad-spectrum antibiotics, e.g. ceftazidime plus gentamicin, plus flucloxacillin if Staph. aureus is suspected. This may be modified according to local guidelines and

re-evaluated

according

to

the

patient’s progress and laboratory guidance.

Granulocyte-colony stimulating factor (rhG-

CSF), i.e. filgrastim, pegfilgrastim (increased dura-

tion of action) or lenograstim, may help in a

severe infection that is responding poorly to

antibiotics. Like other new biological agents it

should

be

used

under

specialist

supervision,

because

it

can

have

serious

side-effects,

e.g.

malaise, bone and muscle pain, exacerbation of

arthritis, sudden onset of severe agranulocytosis,

urinary abnormalities, hepatic enlargement and

spleen enlargement with a risk of spleen rupture.

Immunosuppressive agents, e.g. azathioprine,

cyclophosphamide, ciclosporin and antilymphocyte

globulin, if the condition has an autoimmune

basis.

Corticosteroids are a second-line option because the response to them is very variable and they increase the risk of fungal and viral infection.

Haemostasis, fibrinolysis and anticoagulation

Haemostasis is a vitally important and highly

organized and regulated homeostatic mechanism.

Its function is to secure the optimal flow of blood

to organs and cells under physiological condi-

tions and to respond rapidly to disturbances, e.g.

bleeding caused by tissue damage, and restore

normality. There are four major components that

co-operate sensitively to achieve this result:

•

Vascular endothelium and intima. •

Platelets.

•

Components of the coagulation system. •

Fibrinolytic system.

Commoninvestigations

intotheclotting

cascade are given in Table 11.8.

Vascular endothelium and intima

The endothelium (see Chapter 4) is much more

than an elegant smooth inner lining of the

vessel wall that separates the blood from reactive

components of the intima and minimizes turbu-

lence in the blood, though it does both of these.

In the following discussion, the locations and

functions of individual components of the clot-

ting and thrombolytic pathways are described

first and these are then drawn together when the

clotting cascade is described.

Under normal conditions, it prevents throm-

bosis (clotting),partly

byrepellingcellular

components of the blood by its surface charge. It

also has direct anticoagulant properties due to:

•

Production

of

nitric

oxide,

which

inhibits

platelet adhesion and aggregation and causes

vasodilatation,

thus

maintaining

a

patent blood vessel.

•

Production

of

epoprostenol

(prostacyclin),

which

inhibits

platelet

aggregation,

also

preventing vascular blockage.

•

Presence of heparan and dermatan sulphates,

which are direct anticoagulants.

•

Exoenzymes that break down platelet activa-

tors, e.g. ADP.

•

Thrombomodulin on the surface provides a

high affinity, specific thrombin binding site

and the thrombomodulin-thrombin complex activates protein C 1000-fold (PrCa). PrCa acts as an anticoagulant.

When the endothelium is damaged:

•

Tissue factor (TFr) is exposed and remains

located at the site of damage.

•

Von Willebrand factor (vWF) in the plasma

binds collagen and platelets together via their

GP1b binding sites or collagen binds platelets via their GP1a binding site.

•

Reduced thrombomodulin production results

in less PrCa, which gives reduced anticoagu-

lantactivity

tolimitthrombingeneration,

and

so

prevents

runaway

coagulation.

Protein S acts to bind PrCa to the endothelial

surface.

•Tissue type plasminogen activator inhibitor

is released, which blocks activation of tissue

plasminogen, thus preventing clot lysis and maintaining clot stability.

Platelets

Theseare

derivedfromthe(myeloid)mega-

karyocytes and are an essential component of

haemostasis. They are normally confined to the

vascular lumen by a mutually-repulsive static

charge between them and the vascular endothe-

lium, by the production of nitric oxide and

epoprostenol by the endothelial cells and the

high-velocity laminar flow in the core of the

lumen.

However,

when

the

endothelium

is

damaged,

vWFr

is

exposed

and

binds

the

platelets to collagen, even under conditions of

high

flow.

However,

this

binding

is

not

permanent and the platelets dissociate and roll

slowly along the endothelium. In this situation

the platelets become activated and the platelet

GpIIb-IIIa receptors bind both the vWFr and

fibrinogen,platelet

adhesionbecomesirre-

versible

and

aggregation

occurs,

resulting

in

propagation

of

the

primary

clot.

When

flow

is

reduced,

fibrinogen,

fibronectin (a

large

glycoproteinadhesion

molecule)andcollagen

may

initiate

platelet

adhesion

without

the

intervention of vWFr.

Von

Willebrand’s

disease

(p.

731)

is

an

autosomal-dominant condition, causing either a

deficiency or an abnormal function of vWFr.

Platelet activation

This is caused by the binding of arachidonic acid,

thromboxane A2, ADP, fibrinogen and collagen.

The level of cAMP is reduced and phopholipase C

is activated. The phopholipase generates inositol

triphosphate,

which

mobilizes

calcium,

trig-

gering several calcium-dependent reactions, e.g.

secretion of the contents of platelet granules.

Activation is accompanied by morphological change, the platelets become spherical with large pseudopodia,

followed

by

contraction

of

the cytoskeleton, clot shrinkage and platelet plug

formation (see Chapter 2).

Platelet dysfunction

It is unsurprising from the central role of platelets in clotting that a deficiency of them, i.e. throm-

bocytopenia ( 100 ÷ 109/L, normal 100-500 ÷ 109/L), will lead to bleeding problems, e.g.

•

Moderate haemorrhage after injury.

•Purpura, i.e. spontaneous bleeding into the

skin, usually in the form of a petechial rash, caused

by

numerous

small

bleeds,

which occurs at platelet counts of 20-50 ÷ 109/L (N 150-400 ÷ 109/L). This type of rash does not blanch under pressure, unlike inflammatory rashes, and also accompanies meningococcal meningitis (see Chapter 8).

•

Easy bruising, epistaxis

(nose bleeds), con-

junctival haemorrhage, blood blisters in the

mouth

and

blood

oozing

from

gums

and menorrhagia (heavy periods).

•

In severe disease (

20 ÷ 109/L) there may be

brain and retinal haemorrhage.

Thrombocytopenia may be due to:

•

Inherited abnormalities of platelet function,

e.g. von Willebrand’s disease (see above).

•

Reduced platelet production, e.g. infiltration

of

the

bone

marrow

in

leukaemias

and

lymphomas. Gaucher’s disease is a lysosomal

storage disease, due to abnormal lipid metab-

olism, in which large amounts of lipoids are

deposited in bone marrow and spleen cells,

causingsplenomegaly

andsoexcessive

platelet destruction. It is particularly common

inJews

ofEasternEuropeanorigin (1in

2000-3000 live births).

• Excessive peripheral destruction, due to, e.g.

-

Autoimmune platelet destruction, some-

times with drugs acting as haptens (see

Chapter 2). It may also occur in neonates by

a

process

similar

to

that

causing haemolytic disease of the newborn (HDN; see Chapter 2).

-

Heparin therapy (rarely; see below).

-

Non-immune platelet destruction, e.g. in

hypersplenism,with

orwithoutspleno-

megaly, due

to

alcoholic

cirrhosis,

acute

and chronic infections, e.g. hepatitis (see

Chapter 3), pregnancy, renal failure, endo-

carditis (seeChapters 4 and

8),malaria

and syphilis, and systemic inflammatory

diseases,e.g.

SLE,RAandSjögren’s

syndrome (see Chapter 12).

Other causes may be drugs, e.g. cephalo-

sporins,

penicillins,

quinine,

ciclosporin, mitomycin.

Management of thrombocytopenia includes:

•

Stop any drugs that may be implicated.

•Diagnose and treat any underlying or associ-

ated diseases, e.g. H. pylori infection, hepatitis

C,cytomegalovirus

andHIVinfections.

Treatment of Gaucher’s disease may include

high-dose steroids, infusion of alglucerase and

splenectomy.

•

High-dose

prednisolone,

i.e.

1 mg/kg/day

for

4 weeks, reducing slowly to zero if possible.

About 70% of patients respond, about half of

whom have a long-lasting remission. High-

dosepulsed

dexamethasonehasalsobeen

used.

• Immunosuppressive agents may help in refrac-

tory disease, e.g. azathioprine, mycophenolate

mofetil, ciclosporin, danazol and vincristine.

• Alemtuzumab or rituximab (unlicensed indica-

tions) are monoclonal antibodies, given by IV

infusion, that cause lysis of B-lymphocytes.

Theymay

helpinpatientswithrefractory

autoimmune disease. Although rituximab has

beenused

withminimalside-effects,these

agents

may

cause

severe

anaphylaxis (see

Chapter 2) and should be used under specialist

supervision

with

full

resuscitation

facilities

available.

•

Splenectomy is used as a last resort, espe-

cially in the elderly who may be unfit for

major surgery, but this exposes the patient to recurrent severe infections.

• Children are treated only if there is significant

bleeding. Prednisolone is the first-line therapy

(see above). Chronic disease requires long-

term steroids (with the risk of growth retarda-

tion), IV Ig, or ultimately splenectomy, with a life-long risk of infection. Treatment clearly poses considerable problems.

IV immunoglobulin (IV Ig) gives a prompt but

temporary (3-week) increase in the platelet count.

It is therefore used only in the acute treatment

of

serious

haemorrhage,

usually

with

cortico-

steroids, or to increase the count prior to splenec-

tomy, and so prevent intra-operative bleeding.

There is a risk of unsuspected viral transmission.

Platelet transfusions are not usually beneficial, because they are destroyed rapidly. However, they are used acutely to control life-threatening bleeding, e.g. brain haemorrhage.

Antiplatelet agents

Most anticoagulants affect the venous circula-

tion and have little effect on clotting in the

arteries. Antiplatelet agents reduce platelet aggre-

gation and may inhibit thrombus formation in

the arteries, and so are beneficial in those condi-

tions in which arterial thrombosis is the prime

cause, e.g. MI (see Chapter 4) and some strokes.

They are also useful in embolic diseases, i.e.

vascular blockage caused by clots or clot frag-

fibrinolysis and anticoagulation

729

ments, e.g. pulmonary embolism (PE), retinal vein occlusion and some strokes.

Aspirin

This is readily hydrolysed at blood pH (7.4) to

release acetic acid. Aspirin irreversibly acetylates

a serine residue near the active centre of platelet

cyclo-oxygenase (COX) and therefore prevents

the formation of thromboxane (TX A2), a vaso-

constrictor and potent initiator of platelet acti-

vation.

Because

platelets

have

no

synthetic

ability, the effect is permanent as long as aspirin

is being taken.

For the secondary prevention of thrombotic

IHD and stroke, 150-300 mg is given as soon as

possible

after

the

initial

event

and

this

is

followed by 75 mg daily (low-dose) for lifelong

maintenance.

The use of low-dose aspirin for primary preven-

tion is appropriate only in those in whom the

estimated 10-year risk of CVD and stroke, non-

fatal

and

fatal,

is

20%

(see

BNF

and

the

References and further reading section), provided

that any hypertension is controlled adequately.

In

the

remainder,

the

possible

benefit

is

outweighed

by

the

potential

side-effects,

e.g.

gastrointestinal bleeding. Other uses are in atrial

fibrillation,

provided

there

are

no

other

risk

factorsfor

stroke,anginapectoris (AP)and

intermittent claudication (cramping pain in the

legs due to ischaemia, induced by exercise and

relieved by rest).

Glycoprotein IIb-IIIa ihibitors: abciximab

This monoclonal antibody to GpIIb-IIIa recep-

tors on platelets is used as an adjunct to heparin andaspirin

forthepreventionofischaemic complications in high-risk patients:

•

Those undergoing percutaneous transluminal

coronary

intervention (PTCI),

e.g.

angiog-

raphy or angioplasty (see Chapter 4).

•

Those with unstable angina pectoris (AP) for

the prevention of MI in those scheduled for PTCI. An IV injection is given initially, followed by an IV infusion started 10-60 min before the procedure and continuing for 12 h.

It

should

be

used

only

once

during

the

procedure

because

the

serious

side-effect

of

bleeding, possibly complicated by hypotension,

bradycardia, chest pain, fever, thrombocytopenia and hypersensitivity reactions, are enhanced by repeat dosing.

It is contra-indicated if the patient already has

active

bleeding,

a

bleeding

tendency,

or

thrombocytopenia,

has

had

major

surgery,

intracranial or intraspinal surgery or trauma in

the previous 2 months, stroke within 2 years,

an

intracranial

neoplasm,

arteriovenous

mal-

formation,

aneurysm,

severe

hypertension

or

hypertensive retinopathy, or is breastfeeding.

In view of this long list of potential hazards, it is not surprising that it must be used under

specialist supervision.

In 2002 NICE published guidance on the use of GpIIb-IIIa inhibitors for ACS (Table 11.9).

Glycoprotein IIb-IIIa ihibitors: eptifibatide and tirofiban

These

are

licensed

for

use

with

aspirin

or

heparin to prevent MI in patients with unstable

AP, or those who have non-ST-segment eleva-

tion

MI.

They

have

generally

similar

side-

effects

and

contra-indications

to

abciximab.

However,

eptifibatide

should

be

used

within

24 hof

thelastepisodeofchestpainand tirofibanwithin 12 h.Tirofibanmaycausea reversible thrombocytopenia.

Both agents are given by IV infusion, under specialist supervision, but eptifibatide requires an initial IV loading dose.

Other antiplatelet agents

The thienopyridines, clopidogrel and ticlopidine,

have

similar

actions,

contra-indications

and

side-effects. Ticlopidine is not licensed in the UK.

Clopidogrel is used as a prophylactic oral anti-

coagulant in patients with a history of sympto-

matic ischaemic disease. It is also licensed for use

combined with low-dose aspirin in acute coro-

nary syndrome without ST-segment elevation

(see Chapter 4). In the latter circumstances, the

combination is given for at least 1 month, but

not

usually

for

longer

than 9-12 months.

Readers are directed to the BNF for further details

of interactions, etc. Although clopidogrel should

be initiated only in hospital inpatients, several

trials have reported it to be a safe and effective

alternative to aspirin.

Dipyridamole is used as an adjunct to other

oral

anticoagulation

for

the

prevention

of

thromboembolism

associated

with

prosthetic

heartvalves.

Modified-releasepreparationsare

licensed

for

the

secondary

prophylaxis

of

ischaemic

stroke

and

TIAs.

There

is

no

good

evidence for the benefits of its long-term use with

low-dose

aspirin

in

the

prevention

of

serious

ischaemic cardiovascular events. However, there

is evidence from one trial that this combination

reduces

the

risk

for

non-fatal

stroke,

though

gastrointestinal side-effects were more trouble-

some

and

more

people

withdrew

from

the

combination than from aspirin alone.

Epoprostenol (prostacyclin) may be used in renal

dialysis patients, either alone or with heparin.

Because it is a potent vasodilator it causes flush-

ing, headaches and hypotension. Its half-life is

only about 3 min, so it has to be given by contin-

uous IV infusion, but with these patients it can be

added conveniently to the existing return dialysis

line.

Clotting cascade

Haemostasis

This resembles the complement cascade in that

factors are split to form enzymes or factors with

other activity (see Chapter 2) that act sequentially,

thus giving massive amplification of the initial

reaction. It has been conventional to consider the

clotting pathways as composed of two separate

routes, intrinsic and extrinsic, similar to the situa-

tion with complement. However, the two path-

ways are now known to be integrated in vivo,

forming a unified whole. A summary of these reac-

tions is shown in Figure 11.7. Because there has

been confusion in nomenclature, most of the

various elements are now designated by roman

numerals,

but

these

are

not

numbered

in

sequence. Activated forms are denoted by the

suffix ‘a’.

Tissue factor (TFr) is a glycoprotein that is

expressed constitutively on fibroblast surfaces

and is inducible in endothelial and other cells by

IL-1, TNF and endotoxin, especially if the cells

are damaged. It acts as a co-factor with Factor

VII (FrVII) to initiate the cascade. The FrVII-TFr

complex activates FrIX and FrX, forming FrIXa

and

FrXa.

The

latter

acts

with

FrVa

to

form

the tenase complex (FrXa-FrVa) that converts

prothrombin to thrombin, in association with

phospholipid and Ca2

. Thrombin has the key

role in the process and converts:

•

FrV →

FrVa, to generate additional tenase

complex.

•

Fibrinogen → fibrin.

•FrXIII → FrXIIIa, which in turn crosslinks the

fibrin fibres, forming a stable clot matrix.

•

FrXI → FrXIa, which then converts FrIX →

FrIXa and FrVIII → FrVIIIa. The FrVIIIa-FrIXa

complex converts FrX → FrXa, providing an

fibrinolysis and anticoagulation

731

additional source for the tenase complex that is required because it elicits the production of a tissue factor pathway inhibitor (TFrPI) and inactivates FrVIIa-TFr. The TFrPI is one of the components

that

serves

to

limit

excessive coagulation. The conversion of FrXI → FrXIa may also occur by auto-activation.

FrVIIa is known to bind to platelets indepen-

dently of TFr and causes the release of thrombin

at sites of vascular injury. Although there have

been only a few randomized trials, recombinant

FrVIIa has been reported to be effective in the

management of haemorrhage due to trauma or

surgery, e.g. upper gastrointestinal bleeding (see

Chapter3),

livertransplantsandacuteintra-

cerebral haemorrhage, but these are unlicensed

indications.In

thelattercase,itproduced

improved

outcome

and

reduced

mortality.

It

is

presently

licensed

for

the

treatment

of

haemophilia (see below) and inherited disorders

of platelet function.

Inherited coagulation disorders: haemophilias and von Willebrand disease

The haemophilias are X-linked genetic disorders

of haemostasis that are due to deficiencies of

coagulation factors. There are two forms: the

most common is due to a deficiency of FrVIII:C,

its procoagulant form, which circulates in the

plasma in association with vWFr (see above) and

causes haemophilia A. FrIX deficiency causes

haemophilia B. Because the conditions are X-

linked all affected women are carriers and their

sons have a 50% chance of haemophilia and

daughters

have

a 50%

chance

of

being

a

carrier. However, it is estimated that up to one-

third of mutations in the FrVIII gene may be

spontaneous and so not inherited from a parent.

Because almost all haemophiliacs are male, and

the defective gene is X-linked, all of their daugh-

ters are carriers but all of their sons are normal,

unless the mother is a carrier. A very small

number of women are haemophiliacs, due to

inactivation of the normal chromosomal allele, a

process known as lyonization, very early in

embryo development.

The prevalence of haemophilia A is about 1 per 5000-10 000 and haemophilia B is about

one-fifth as common.

The FrVIII gene is very large (186 kilobases) and

numerous mutations have been identified that

may produce a range of levels of functionality,

the normal range of FrVIII level being 50-200%

of the mean. The FrIX gene is much smaller (33

kilobases) and is inherited similarly to FrVIII,

though recessive forms also occur. Some muta-

tions give rise to the ‘Leyden’ phenotype that

disappears after puberty.

Deficiency of vWFr, the functions of which are

describedon

p. 726,alsocausesableeding

tendency that may vary from mild to severe.

Theyare

muchmorecommonthanthe

haemophilias and the prevalence of mild von

Willebrand disease (vWD) is estimated to reach

1% in some populations. This high frequency is

a reflection of its dual roles in FrVIII:C carriage

and platelet binding to vascular endothelium.

There are three forms of vWD, the genes for

which are located on chromosome 12, two genes

being inherited as autosomal dominant alleles,

and the other recessive.

Clinicalfeatures.

Alloftheseconditions confer a haemorrhagic tendency, and bleeding may be spontaneous, e.g. epistaxis or bleeding from the gums and mouth, or occur after minor trauma, e.g. dental treatment, or surgery.

Haemophilia A and B cannot be distinguished

clinically. Children with haemophilia are usually

healthy at birth, though excessive cord bleeding

and heavy bruising due to birth trauma may

occur. Symptoms develop towards the end of the

first year, especially bruising, but spontaneous

bleeds

become

less

frequent

in

adults.

The

popular idea that patients ‘bleed to death’ after

minor trauma is incorrect, though intracranial

haemorrhage may be life-threatening. The major

problem is bleeding into muscles and weight-

bearingjoints (haemarthrosis)

andrecurrent

joint bleeds may cause serious damage there.

Patientsshould

notbegivenIMinjec-

tions.

Bleeding

after

trauma

usually

requires

therapeutic intervention.

Both

sexes

are

affected

in

vWD.

Mucosal

bleeding

and

bleeding

after

trauma

or

sur-

gery

are

the

principal

problems

but,

unlike

haemophilia, bleeding into joints and muscles

occurs

only

rarely.

Menorrhagia

may

present

problems in fertile women. Patients with milder

fibrinolysis and anticoagulation

733

diseasemay

notpresentuntiltheirthirdor fourth decade.

Management of haemophilia.

Genetic coun-

selling is an essential component of the care of

affected families, and genetic analysis is available

for the detection of carriers. Antenatal diagnosis

is also used to detect those who have slipped

through the net, especially recent immigrants.

Management involves detection of the partic-

ular clotting factor deficiency and its replace-

ment. In the 1980s and 1990s, freeze-dried factor

concentrates were prepared from large donor

pools, but these transmitted unsuspected viral

infection to some patients, especially hepatitis

and HIV. This was countered by careful donor

selection, viral inactivation by irradiation and

immunization against hepatitis. However, there

was still concern about the possibility of trans-

mission of variant Creutzfeld-Jakob disease, and

recombinant human FrVIII and FrIX (rhFrVIII,

rhFrIX) are now available and have replaced

concentrates from plasma.

Unfortunately, inhibitory antibodies to FrVIII

are

formed

in

about

10%

of

treated

patients

and has required desensitization treatment in

specialized

centres (see

Chapter 2).

These

inhibitors are active against both endogenous

factors and those given therapeutically and cause

severe problems in treatment. The problem has

beenexacerbated

bytheadministrationof

rhFrVIII because it is not complexed with its

carriermolecule (vWFr)

andconsequentlyis

more immunogenic. Inhibitor formation occurs

only rarely with FrIX. Recombinant activated

FrVII overcomes the inhibitor problem in both

types of haemophilia, because it bypasses the

reactions that require FrVIII and FrIX in the

clotting cascade (Figure 11.7). It is licensed for

the treatment of haemophilia patients in whom

inhibitors have developed.

Vasopressin,

the

ADH,

and

its

more

potent,

longer-acting

analogue

desmopressin

stimulate

the release of FrVIII (and vWFr) from endothelia

and WBCs and are used in mild to moderate

haemophilia

A

to

reduce

the

need

for

exog-

enous FrVIII. Vasopressin is used with an anti-

fibrinolytic

agent,

e.g.

tranexamic

acid,

which

boosts

its

effect.

The

latter

is

also

used

to

control

bleeding

due

to

minor

procedures

in haemophiliacs, e.g. dental extractions, but are not used with FrIX because of the thrombotic risk. Antifibrinolytic agents (see below) are also used with rhFrVIII to assist in the control

of

external bleeding.

Modulation of haemostasis - intrinsic

anticoagulant pathways and fibrinolysis

These are an integral part of the clotting cascade and

provide

for

control

of

haemostasis,

to prevent excessive coagulation that could com-

promise the circulation, and for the removal of the clot when it has fulfilled its functions of

preventing haemorrhage and providing a support matrix for vascular wall repair.

Intrinsic anticoagulant pathways include:

•

TFrPI, mentioned above.

• Antithrombins (serpins), which block the

activation of FrV, FrVIII, FrXI and the conver-

sion of fibrinogen to fibrin.

•

Heparin,

which

potentiates

the

action

of

antithrombins against FrXa and thrombin,

the activity of antithrombins being increased 2000-fold.

•

Thrombin probably binds to thrombomod-

ulin that is bound to endothelial cell surfaces.

When bound, thrombin loses its procoagu-

lant

properties

and

is

transformed

into

a highly active anticoagulant.

•

The

thrombin-thrombomodulin

complex

vastly increases the activation rate of protein

C (PrC). The PrCa breaks down FrVa and

FrVIIIa and so inhibits additional thrombin production.

• The PrCa, together with its co-factors protein

S (PrS) and Ca2

, binds to phospholipid on

cell surfaces and so prevents the conversion of prothrombin

to

thrombin

by

the

tenase

complex.

•

FrXIIIa binds alpha2-antiplasmin to fibrin and

may protect the clot from fibrinolysis.

Fibrinolysis

Solution of the platelet-fibrin clot is an essential

sequel to clotting and removes the clot when

vascular repair has occurred and the clot is no

longer needed. Tissue type plasminogen acti-

vator (tPA)

is secreted from endothelial cells

and, bound to fibrin, converts plasminogen to

plasmin,

which

activates

tPA

by

splitting

it

into a double-stranded molecule. Plasmin also

hydrolyses

FrV,

FrVIII,

FrXIII,

fibrinogen

and

fibrin.

The

latter

yields

fragment

X,

which

inhibits thrombin, and fragments Y, D and E,

which

inhibit

fibrin

polymerization.

Alpha2-

antiplasmin and tPA are inhibited, thus prevent-

ing undue fibrinolysis, fibrinogen consumption

and haemorrhage.

A diagram of the fibrinolytic pathways is given in Figure 11.8.

It is apparent from the foregoing account that

the

numerous

steps

and

counteracting

factors

involved in the haemostatic and fibrinolytic path-

ways enable the processes to be controlled with

exquisite sensitivity to produce a response tailored

precisely to the requirements of local situations.

Recombinant

tissue-type

plasminogen

acti-

vator (rt-PA, alteplase) is used for clot dissolution

in

acute

myocardial

infarction (AMI) (see

Chapter 4),pulmonary

embolism (PE,see

Chapter 5)

and,

under

the

supervision

of a

specialist

neurological

physician,

for

acute

ischaemic stroke. It is administered by IV injec-

tion, followed by IV infusion. Alteplase treatment

for AMI (see Chapter 4) must be given within 3 h

to be of maximal benefit, the earlier the better

to

minimize

permanent

myocardial

damage.

Reteplase and tenecteplase are also licensed for use

in AMI and have the advantage of being given by

IV injection only, without the need for IV infu-

sion. Fibrinolytics are especially beneficial in

thosewith

STsegmentelevationorbundle

branch block (see Chapter 4).

Reteplase is licensed for the thrombolytic treat-

ment of AMI and should be given within 12 h. Heparin and aspirin are administered both before using reteplase and afterwards, to minimize the risk of re-infarction.

Immediate MRI/CT imaging will distinguish

between

thromboembolic

and

haemorrhagic

strokes. Serious exacerbation of bleeding results if

lytic agents or anticoagulants are used in unsus-

pected haemorrhagic stroke. Imaging will also

demonstrate the presence of occult pathology,

e.g.

a

tumour

or

rapidly

enlarging

aneurysm,

and trauma, which are contra-indications to the

use of alteplase, etc. Other exclusion criteria are

recent

major

surgery,

recent

MI

and

bacterial

endocarditis (see Chapter 8).

Streptokinase, another plasminogen activator

prepared from streptococci, is used for MI, PE,

DVT,

acute

arterial

thromboembolism

and

centralretinal

arteryorveinthrombosis.

Although much cheaper than the other agents,

it has the disadvantage that it produces a persis-

tent allergic state and cannot be used repeatedly

in

a

patient

without

special

precautions.

Anaphylaxis and Guillain-Barré syndrome are

serious side-effects.

Many patients with branch retinal vein throm-

boembolismdo

notrequirethrombolytic therapy and do well with no treatment or aspirin antiplatelet therapy and end up with only minor retinal scarring.

The sites of action of these agents are shown in Figure 11.8.

Antifibrinolyticagents

maybeusedto

prevent excessive blood loss in surgical proce-

dures. The use of tranexamic acid in haemophilia

is

referred

to

above.

It

is

given

by

slow

IV

injection in prostatectomy and orally in menor-

rhagia and hereditary haemorrhagic telangiec-

tasia. The latter is a rare, autosomal-dominant

condition in which there are widespread collec-

tionsof

dilatedcapillariesandarteriolesthat

bleed easily. They are visible as a skin rash that

blanches under pressure and in the mouth, lips,

nasal mucosa and on the tips of the fingers and

toes. Recurrent profuse epistaxis and gastroin-

testinal

bleeding

cause

anaemia,

but

the

first

presentation may be an embolic TIA or stroke.

Tranexamic

acid

is

contra-indicated

in

severe

renal

disease

and

thromboembolic

states

and should be used with caution in severe haema-

turia because it may cause ureteric clotting and obstruction.

Aprotinin is a proteolytic enzyme inhibitor that

acts on plasmin and kallikrein. It is given by

slow IV injection or infusion in major surgery,

e.g. open heart surgery, tumour resection and

following thrombolytic therapy (see above). Its

use in liver transplantation is unlicensed.

Etamsylateis

anotherantifibrinolyticagent

that is licensed for the prevention of blood loss

inmenorrhagia.

Itreducescapillarybleeding

if

there

is

a

normal

platelet

count,

probably

by

correcting

abnormal

platelet

adhesion

to

endothelium.

Procoagulable states - antiphospholipid syndrome

This is an autoimmune, connective tissue type

disorder (see Chapters 2 and 12) that is charac-

terized

by

antibodies

against

cell

membrane

phospholipids. It is sometimes associated with

SLE (see

Chapter 12).

Because

of

this,

and

becausethe

antibodiesalsoreactwiththe

artificial antibody cardiolipin that was used in

the old Wasserman test for syphilitic antibodies,

they have been called ‘lupus anticoagulant’ and

‘anticardiolipin’.

Aetiology, clinical features and pharmacotherapy

The autoantibody target is beta2-glycoprotein

(b2-GP1), sometimes known as apolipoprotein H.

The autoantibodies are known to reduce the

levels of annexin V, a surface adhesion protein

that occurs in vascular endothelium and the

placenta.

Clinical features.

There are recurrent arterial and venous thromboses, causing about 20% of strokes occurring before the age of 45. Adrenal gland thrombosis may cause Addison’s disease. Placental clotting is responsible for about 30% of miscarriages in women who have suffered two or more spontaneous abortions.

There is the paradoxical situation of a pro-

thrombotic state in vivo and antibodies that have

an anticoagulant effect in vitro, the reason for

which is unknown. Other features are migraine,

epilepsy

and

other

CNS

effects,

heart

valve

disease and the skin rash, livedo reticularis, a

net-like pinkish rash surrounding pale areas of

skin, showing the pattern of the blood supply in

the epidermis.

Investigations.The antibodies are detected by enzyme-linked immunosorbent assay. The ESR and antinuclear antibody tests (ANA; see Chapter 12) are usually negative. The direct Coomb’s test (Figure 11.6) is positive.

Treatment is with aspirin, if mild, or warfarin

if moderate to severe (see below). Heparin has

to

be

substituted

for

warfarin

in

pregnancy,

which should be managed by a gynaecological

specialist.

Therapeutic anticoagulation

The purpose of this treatment is to prevent:

•Venous and arterial clotting and clot propaga-

tion, e.g. in antiphospholipid syndrome (see

above).

•

Clotting in the cardiac chambers or coronary

circulation, e.g. in atrial fibrillation and on

prosthetic heart valves.

•

Embolization from these clots, e.g. causing

stroke or PE. Clotting in the brain.

Patient assessment

Relative contra-indications include:

•

Recent major surgery or traumatic injury, a

bleeding tendency, active bleeding, e.g. from

a peptic ulcer (see Chapter 3), or a family

history of excessive bleeding.

•

Inadequately

controlled

hypertension

(see

Chapter 4).

•

Severe

hepatic

or

renal

dysfunction.

Liver

disease causes a deficiency of erythropoietic

factors and important clotting proteins. Both

liver and kidney diseases result in deficiencies

of erythropoietin and thrombopoietin (see

Chapter 2).

•Drug abuse, if injections are used.

•

Alcohol

abuse,

which

may

cause

gastric

bleeding and dementia and damages the liver.

•

Heparin may cause a hypersensitivity reaction

andisunsuitableinthrombocytopenia

because it reduces the platelet count.

Many of these conditions are amenable to

treatment and anticoagulation should not be

initiateduntil

appropriatetherapyhasbeen given or until wounds are healed.

A medication history must be taken and any

potential interactions considered, e.g. are the

drugs essential or can alternatives be used? This

is particularly important if warfarin therapy is

contemplated

because

its

activity

may

be

enhanced or reduced by a very large number of

other

agents,

including

aspirin

and

NSAIDs,

alcohol, herbal remedies (e.g. St John’s wort) and

dietary changes (appropriate references should

be consulted for a comprehensive listing).

Although analgesic doses of aspirin are contra-

indicated

in

those

taking

warfarin,

low-dose aspirin (75 mg/day) is acceptable in those at risk of thromboembolism, provided that the dose of warfarin is determined (see below) while the

patient is taking the aspirin. It should be remem-

bered that clotting changes occur both when

starting aspirin and if it is stopped.

Warfarin is a potent teratogen and causes severe

fetal deformity, especially if taken in weeks 6-12

of gestation, when organogenesis is occurring.

However, the use of all antiplatelet drugs at any

stage of pregnancy may cause miscarriage or some

degree of fetal malformation. Heparins do not

cross

the

placenta

but

may

cause

undesirable

problems in the mother, e.g. a reduced platelet

count, hyperkalaemia due to inhibition of aldo-

sterone secretion, skin necrosis, hypersensitivity

reactionsincluding

anaphylaxisandosteo-

porosis. Low molecular weight heparins are safer,

but their use with prosthetic heart valves has been

contentious.

Preliminary investigations are listed in Table

11.9.

Warfarin management

Pharmacology.

Warfarin

is

the

standard

coumarin oral anticoagulant in the UK. Aceno-

coumarol (nicoumalone) is used occasionally, as is phenindione, a non-coumarol.

Warfarin

inhibits

the

carboxylation

of

the

vitamin K-dependent clotting factors, i.e. FrII,

fibrinolysis and anticoagulation

737

FrVII,

FrIX

and

FrX,

and

the

coagulation inhibitor proteins, i.e. PrC and its cofactor PrS (see above).

It is readily absorbed, the peak plasma level is

achieved at about 1.5 h, and the onset of action

is at about 48 h (24-72 h). Because of its once-

daily dosing, steady-state levels are not reached

for about 5 days. Accordingly a loading dose is

given for the first 4 days of treatment. It is 97%

bound to plasma proteins, displacement being

the basis of its interactions with other acidic

drugs.The

half-lifeisveryvariablebetween

individuals, being in the range 24-72 h.

Therapy is monitored using the international

normalized

ratio

(INR; Table 11.8),

which

is

theratio

ofthepatient’sprothrombintime

(PT)

to

that

of

a

normal

control,

using

stan-

dardized

reagents.

Recommended

target

levels

for various conditions are given in Table 11.10.

Induction.

The initial loading dose is deter-

mined according to the baseline PT and should

be reduced if this is prolonged (normal values:

PT 12-16 s, INR 1.0-1.3), if the patient’s liver

function tests are abnormal, if the patient is

elderly or in cardiac failure, is on parenteral

feeding, has a low body weight and is taking

drugs

known

to

potentiate

warfarin

activity.

Although

the

normal

initial

loading

dose

is

given in the BNF as 10 mg/day for 2 days, the

British Guidelines on Oral Anticoagulation (see

References and further reading, p. 741) recom-

mend 5 mg/day for 4 days. All recommendations

here are based on these guidelines.

High loading doses produce rapid reductions

in the levels of the anticoagulant proteins C and

S (see above and Figure 11.8) and may cause SC

thrombosis

and

skin

necrosis.

Accordingly

heparin (see below) is given to patients at high

risk

of

thromboembolism

before

initiating

warfarin, e.g. in atrial fibrillation (see Chapter 4)

or if there is a personal or family history of

venous thrombosis. This should be continued

until the INR is2 for 2 days. In such cases the

startingdose

ofwarfarinshouldnotexceed

5 mg/day.

Maintenancedosing.

Theaverageis3to

9 mg/day,

but

this

varies

very

widely

(0.5

to

25 mg/day, and the required dose is managed on a ‘sliding scale’, e.g. Table 11.11.

Problems with warfarin.

Most serious bleeds

occur at the target INR and the bleeding risk

increases

exponentially

with

INR

values

5.

Treatment of bleeds depends on their site and

severity. For major haemorrhage the following

are appropriate.

•

Stop warfarin and determine a baseline INR.

Determine and treat the cause of bleeding,

e.g.

unsuspected

renal,

hepatic

or

gastro-

intestinal problems.

•

Give prothrombin concentrate (FrII

FrVII

FrIX

FrX)

up

to

50 units/kg,

depending

on

the

INR,

or

fresh

frozen

plasma

(FFP)

15 mL/kg.

•

Give phytomenadione (vitamin K1) 5-10 mg by

slow IV injection and repeat after 24 h if the

INR is still high. The degree of reversal is

determined by the severity of the bleed. It is preferablenot

toreverseanticoagulation completely, because warfarin resistance may then occur, and it may be advisable to halve the starting dose of phytomenadione.

•

When bleeding has been controlled, monitor

the INR and resume warfarin at a lower dose.

For

minor

bleeds,

e.g.

epistaxis,

sub-

conjunctival haemorrhage, bruising and mild

haematuria, it is sufficient to stop or reduce

warfarin until the bleeding is controlled.

For a high INR without bleeding, the Guide-

lines recommend:

•

INR

8: stop warfarin

until INR

5. Give

phytomenadione PO if there are any risk factors

for bleeding, e.g. liver or kidney dysfunction,

uncontrolled

peptic

ulceration

or

hyper-

tension, a personal or family history of bleed-

ing problems, or a non-concordant patient.

However, phytomenadione

is oil-soluble and

oral dosing is not suitable for people with

malabsorption (see Chapter 3). Slow IV injec-

tion of a micellar formulation is suitable in

these patients.

•

INR

6-8:

stop

warfarin

for

1-2 days

and

recommence at a lower dose.

•

INR

6 but more than 0.5 above target level:

stop or reduce warfarin

until INR

5 and

recommence at a lower dose.

•

INRs within

0.5 of the target level are

acceptable and do not require action.

•

Cancer patients and those who have had a

venousthromboembolism (VTE)areat

significant

risk

of

further

thrombosis

despite

appropriate

warfarin

treatment.

Trials

have

shown

that

low

molecular

weight heparins (LMWHs) halve the risk of

recurrent

VTE

compared

to

warfarin,

with

noincrease

inmortalityorbleeding

episodes.

The

BCSH

guidelines

state

that

LMWHs

are

superior

to

warfarin

in

cancer

patients.

Because of these problems and the costs and

inconvenience of warfarin

management there

have been numerous unsuccessful attempts at

producing an oral warfarin replacement that is

more predictable in use and so does not require

close monitoring. The only agent that was intro-

duced, ximelagatran, has been withdrawn perma-

nently due to its potential to cause severe liver

damage.

All patients taking oral anticoagulants should

be issued with a treatment booklet that gives

the

patient

advice

on

their

treatment

and

provides a diary of all doses that have been used.

This should be carried at all times as an alert to

doctors in the event of trauma requiring hospital

treatment.

Heparins

Pharmacology

of

heparin.

Unfractionated

heparin

is

a

glycosaminoglycan

produced

by

mast cells that is extracted from porcine mucosa.

It is therefore unsuitable for strictly observant

Jews and Muslims. Heparan sulphate is a related

compound found in the extracellular matrix of most eukaryotic cells.

Heparin has a rapid onset of action and a short

duration of effect. It consists of heterogeneous

chains

of

molecular

weight 2-30 kDa.

Most

preparations can be given by IV or SC injection,

but Calciparine (a proprietary heparin product)

can be used only by the SC route. Some indica-

tions for heparin use are given in Table 11.12.

An

important

side-effect

of

heparin

use,

including

LMWHs (see

below),

is

immune-

mediatedheparin-induced

thrombocytopenia

(HIT)

that

normally

occurs

after 6-14 days’

treatment and causes a paradoxical thrombosis.

Thus platelet counts should be done for patients

in whom heparins are to be used for 5 days.

A platelet count of

50%

of normal requires

immediate

withdrawal

of

the

heparin.

If

continued anticoagulation is required, it should

be replaced with a heparinoid or lepirudin (see

below).

Rapid reversal of heparin activity requires the

administration of protamine sulphate, a specific

antidote. LMWHs are reversed only partially by

protamine sulphate and their duration of action is

longer.

Inhibition

of

aldosterone

secretion

by

heparins may result in hyperkalaemia (see Chap-

ters 2, 4 and 5), with adverse cardiac effects, so

prolonged therapy requires serial plasma potas-

sium measurements. Mild to moderate hyper-

kalaemiacan

betreatedwithapolystyrene

sulphonate ion exchange resin, but glucose plus

insulin is needed if a more rapid reduction in

potassium level is required (see Chapter 9).

LMWHs, i.e. bemiparin, dalteparin, enoxaparin,

reviparin

and

tinzaparin,

are

produced

from

unfractionated heparin by depolymerization and

have a molecular weight of 3-6 kDa. They are

generally as effective and safe as unfractionated

heparin

for the prophylaxis of venous throm-

boembolism and are probably more effective thanunfractionated

heparininorthopaedic surgery. Some indications for their use are given in Table 11.12.

Because they have a longer duration of action than

unfractionated

heparin

they

are

given conveniently by once-daily SC injection.

Heparin activity is monitored using the acti-

vated

partial

thromboplastin

time (APTT),

but this is not needed if heparins are used in

well-defined standard prophylactic regimens.

Other antithrombotic agents

Danaparoid sodium is a heparinoid that is licensed

for the prevention of DVT in general surgery and

in patients with HIT (see above). However, it is

not clear whether there is a cross-reaction with

heparins.

Bivalirudin

and

lepirudin

are

recombinant hirudins, i.e. they are the biogenetic analogues of hirudin, the anticoagulant that enables leeches (Hirudo

medicinalis)

to

maintain

blood

flow when feeding on animals. Their use is monitored by APTT, not INR.

Bivalirudin is licensed for use in patients under-

going percutaneous coronary angiography and angioplasty (see Chapter 4). The Scottish Medi-

cines Consortium have approved it for restricted use in patients undergoing percutaneous coro-

nary interventions who would have been consid-

ered for treatment with unfractionated heparin plus a platelet GPIIa-IIIb inhibitor, i.e. abciximab, eptifibatide

and

tirofiban.

Lepirudin

is

licensed only for use in patients with HIT.

References and further reading741

Fondaparinux

sodium

is

a

new

synthetic

pentasaccharide FrXa inhibitor that is licensed

for the prophylaxis of venous thromboembolism

in medical patients, those undergoing abdom-

inal surgery and major orthopaedic surgery of

the legs.