Page 326 - Textbook of Pathology, 6th Edition

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SECTION II

Figure 12.21 Diagrammatic representation of classification of haemolytic anaemias based on principal mechanisms of haemolysis.

Most of the abnormalities due to vitamin B deficiency Extravascular haemolysis is more common than the
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can be corrected except the irreversible damage to the spinal former. One or more factors may be involved in the
cord. Corticosteroid therapy can improve the gastric lesion pathogenesis of various haemolytic anaemias.
with a return of acid secretion but the higher incidence of Haemolytic anaemias are broadly classified into 2 main
gastric polyps and cancer of the stomach in these patients categories:
can only be detected by frequent follow-up. I. Acquired haemolytic anaemias caused by a variety of
extrinsic environmental factors (extracorpuscular).
HAEMOLYTIC ANAEMIAS
II. Hereditary haemolytic anaemias are usually the result of
GENERAL ASPECTS intrinsic red cell defects (intracorpuscular).
A simplified classification based on these mechanisms is
Definition and Classification given in Table 12.9 and diagrammatically represented in
Fig. 12.21.
Haemolytic anaemias are defined as anaemias resulting from
an increase in the rate of red cell destruction. Normally, effete Features of Haemolysis
red cells undergo lysis at the end of their lifespan of 120+30
days within the cells of reticuloendothelial (RE) system in A number of clinical and laboratory features are shared by
the spleen and elsewhere (extravascular haemolysis), and various types of haemolytic anaemias. These are briefly
haemoglobin is not liberated into the plasma in appreciable described below:
Haematology and Lymphoreticular Tissues
amounts. The red cell lifespan is shortened in haemolytic GENERAL CLINICAL FEATURES. Some of the general
anaemia i.e. there is accelerated haemolysis. However, clinical features common to most congenital and acquired
shortening of red cell lifespan does not necessarily result in haemolytic anaemias are as under:
anaemia. In fact, compensatory bone marrow hyperplasia
may cause 6 to 8-fold increase in red cell production without 1. Presence of pallor of mucous membranes.
causing anaemia to the patient, so-called compensated 2. Positive family history with life-long anaemia in patients
with congenital haemolytic anaemia.
haemolytic disease.
The premature destruction of red cells in haemolytic 3. Mild fluctuating jaundice due to unconjugated
anaemia may occur by 2 mechanisms: hyperbilirubinaemia.
4. Urine turns dark on standing due to excess of
Firstly, the red cells undergo lysis in the circulation and
release their contents into plasma (intravascular haemolysis). urobilinogen in urine.
In these cases the plasma haemoglobin rises substantially 5. Splenomegaly is found in most chronic haemolytic
and part of it may be excreted in the urine (haemoglobinuria). anaemias, both congenital and acquired.
6. Pigment gallstones are found in some cases.
Secondly, the red cells are taken up by cells of the RE
system where they are destroyed and digested (extravascular LABORATORY EVALUATION OF HAEMOLYSIS.
haemolysis). In extravascular haemolysis, plasma Pathways by which haemoglobin derived from effete red cells
haemoglobin level is, therefore, barely raised. is metabolised is already discussed on page 290. The