Haemolytic anaemia I – General features and inherited disorders

General features of haemolysis

The term ‘haemolytic anaemia’ describes a group of anaemias of differing aetiology that are all characterised by abnormal destruction of red cells. The hallmark of these disorders is reduced lifespan of the red cells rather than underproduction by the bone marrow.

In classification of the haemolytic anaemias there are three main considerations:

The mode of acquisition of the disease: is it an inherited disorder or a disorder acquired in later life?

The location of the abnormality: is the abnormality within the red cell (intrinsic) or outside it (extrinsic)?

The site of red cell destruction: red cells may be prematurely destroyed in the bloodstream (intravascular haemolysis) or outside it in the spleen and liver (extravascular haemolysis).

The simple classification in Table 14.1 relies upon division of the main clinical disorders into inherited and acquired types. In general, it can be seen that inherited disorders are intrinsic to the red cell and acquired disorders extrinsic. The inherited disorders can be subdivided depending on the site of the defect within the cell – in the membrane, in haemoglobin, or in metabolic pathways. Acquired disorders (discussed in the next section) are broadly divided depending on whether the aetiology has an immune basis.

Table 14.1

Classification of the haemolytic anaemias

Inherited disorders
Red cell membrane	Hereditary spherocytosis and hereditary elliptocytosis
Haemoglobin	Thalassaemia syndromes and sickling disorders
Metabolic pathways	Glucose-6-phosphate dehydrogenase and pyruvate kinase deficiency
Acquired disorders
Immune	Warm and cold autoimmune haemolytic anaemia
Isoimmune	Rhesus or ABO incompatibility (e.g. haemolytic disease of newborn, haemolytic transfusion reaction)
Non-immune and trauma	Valve prostheses, microangiopathy, infection, drugs or chemicals, hypersplenism