Page 500 - Medicine and Surgery

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496 Chapter 12: Haematology and clinical immunology

azathioprine, vincristine and danzol. Platelet transfu- Clinical features
sions are only used in life threatening haemorrhage. Dilation of small arteries and capillaries result in charac-
teristic small red spots that blanch on pressure (telang-
iectasia) in the skin and mucous membranes particularly
Thrombotic thrombocytopenia the nose and gastrointestinal tract. Patients suffer from
purpura
recurrent epistaxis and chronic gastrointestinal bleeds.
See page 252.
Complications
Patients are prone to chronic iron deficiency anaemia.
Thrombotic disorders

Thrombophilia
Transfusion medicine
Definition
Thrombophilia is a group of disorders resulting in an Transfusion medicine
increased risk of thrombosis.
FactorVLeiden(ActivatedProteinCresistance):This Blood grouping

is the commonest form of thrombophilia. It is present Grouping is the process by which the patient’s ABO and
in 2–3% of the population and results from a point rhesus D status are determined. The patient’s blood sam-
mutation in the factor V gene. The mutation results ple is separated into cells and serum. These are grouped
in a resistance of factor V to inactivation by Protein C. separately in order to act as a double check.
This failure in the normal control of the coagulation The patient’s red cells are incubated with commercial
cascade results in a thrombotic tendency. This risk is antibodypreparationsagainsttheA,BandDantigens.
further increased in homozygotes, in women taking By examining the pattern of agglutination the blood
the oral contraceptive pill and in pregnancy. group can be determined.
ProteinC&Sdeficiency,AntithrombinIIIdeficiency:
The patients serum is incubated with red cells of
Deficiency in normal factors that downregulate the known blood group (A, B, AB and O Rh ) and the
+
coagulationcascadeincreaseclottingtendency.Inher- agglutination patterns are read to check the blood
itance of a single mutation for any of these conditions group.
results in recurrent thrombotic episodes in young pa-
tients. Antibody screening
Forclinical features and management of venous throm- The patient’s serum is also tested for atypical red cell an-
boembolism see page 81. tibodiesusingatleasttwoGroupOdonorswhoexpressa
wide range of antigens. Any IgM antibodies present will
automatically agglutinate the donor red cells suspended
Anti-phospholipid syndrome
in saline (see Fig. 12.13). IgG antibodies are detected by
See page 367. the indirect Coomb’s test (see Fig 12.14).

Cross matching
Vascular causes of bleeding
Agroup matched blood unit (antigen matched if patient
See also Henoch Sch¨ onlein Purpura (see page 381). has atypical antibodies) is cross matched with the pa-
tient’s serum. A full cross match consists of incubating
the patient’s serum with the donor red cells and then
Hereditary haemorrhagic
telangiectasia performing a direct agglutination and indirect Coomb’s
test as above. In an emergency, if the patient has no atyp-
Definition ical antibodies a rapid cross match can be performed by
Rare autosomal dominant vascular disorder resulting in briefly incubating the patient’s serum with the donor
telangiectasia and recurrent bleeding. cells and examining for agglutination.