Page 101 - Essential Haematology

Chapter 6 Haemolytic anaemias / 87

factor (DAF, CD55) and membrane inhibitor of immunologically mediated, against cells that have
reactive lysis (MIRL, CD59) render red cells sensi- normal GPI - linked membrane proteins.

tive to lysis by complement and the result is chronic PNH is diagnosed by flow cytometry which
intravascular haemolysis. Haemosiderinuria is a shows loss of expression of the GPI - linked proteins,
constant feature and can give rise to iron defi ciency CD55 and CD59. Alternatively, a test for loss
which may exacerbate the anaemia. CD55 and of the GPI anchor on WBC (FLAER) may be
CD59 are also present on white cells and platelets. used.
The other main clinical problem seen in PNH is Eculizumab, a humanized antibody against

thrombosis and patients may develop recurrent complement C5, inhibits the activation of terminal
thromboses of large veins including portal and components of complement and reduces haemoly-
hepatic veins, as well as intermittent abdominal sis and transfusion requirements. Iron therapy

pain brought about by thrombosis of mesenteric is used for iron deficiency and long - term anti-
veins. coagulation with warfarin may be needed.
PNH is almost invariably associated with some Immunosuppression can be useful and allogeneic
form of bone marrow hypoplasia, often frank aplas- stem cell transplantation is a defi nitive treatment.
tic anaemia. It appears that the PNH clone may The disease occasionally remits and the median sur-

expand as a result of a selective pressure, possibly vival is approximately 10 years.

■ Haemolytic anaemia is caused by transfusion), there is haemoglobinaemia,

shortening of the red cell life. The red cells methaemalbuminaemia, haemoglobinuria
may break down in the reticuloendothelial and haemosiderinuria.
system (extravascular) or in the circulation ■ Genetic defects include those of the red SUMMARY

(intravascular). cell membrane (e.g. hereditary
■ Haemolytic anaemia may be caused by spherocytosis), enzyme defi ciencies (e.g.

inherited red cell defects, which are usually glucose - 6 - phosphate dehydrogenase or
intrinsic to the red cell, or to acquired pyruvate kinase defi ciency) or
causes, which are usually caused by an haemoglobin defects (e.g. sickle cell
abnormality of the red cell environment. anaemia).

■ Features of extravascular haemolysis ■ Acquired causes of haemolytic anaemia
include jaundice, gallstones and include warm or cold, auto - or allo -
splenomegaly with raised reticulocytes, antibodies to red cells, red cell
unconjugated bilirubin and absent fragmentation syndromes, infections, toxins
haptoglobins. In intravascular haemolysis and paroxysmal nocturnal
(e.g. caused by ABO mismatched blood haemoglobinuria.

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