The normal red cell membrane consists of a lipid bipolar layer, vertical penetrating proteins and a horizontal protein skeleton consisting of α and β spectrin and proteins that join them to each other (Fig. 14.1).
This is the most common inherited haemolytic anaemia (HA) in white people. It is autosomal dominant with variable severity and may present as severe neonatal HA, as symptomatic HA later in life or may be an incidental finding. Defect is in a red cell membrane protein, e.g. ankyrin, band 3 or β-spectrin; 25% of cases are new mutations. Affected red cells lose membrane during passage through the reticuloendothelial system, especially the spleen. The cells become progressively more spherical (decreased surface area : volume ratio) and microcytic. They are destroyed prematurely, mainly in the spleen. Hereditary elliptocytosis (HE) is a similar, usually milder, abnormality, usually due to mutations of α or β spectrim.
Clinical features are those generally associated with HA. The spleen is usually enlarged.
- Blood film: microspherocytes and polychromasia (Fig. 14.1).
- Haemoglobin level variable.
- Tests for HA are positive (see Chapter 13).
- Special test: Eosin-5-maleimide (EMA) test for band 3 abnormality usually positive (Fig. 14.2). This uses flow cytometry to determine the amount of fluorescence, affecting EMA binding to membrane proteins.
- Direct antiglobulin test is negative, excluding warm autoimmune HA which can cause a similar blood film appearance.