Haemolytic anaemia: diagnostic approach: Case

Case discussion

Diagnosis and immediate assessment

This boy presents chronic compensated haemolysis with the classic clues to hereditary spherocytosis: intermittent jaundice worse with illness, splenomegaly, a father with a splenectomy and gallstones, spherocytes on the film, a raised mean corpuscular haemoglobin concentration, and a negative direct antiglobulin test that excludes autoimmune haemolytic anaemia. The first step is to confirm the diagnosis with the recommended flow cytometric screen rather than relying on the film alone, because spherocytes also appear in warm autoimmune haemolytic anaemia and the distinction rests on the direct antiglobulin test and the confirmatory assay. ^[1]

Confirmatory testing

The International Council for Standardization in Haematology recommends eosin-5-maleimide binding flow cytometry as the preferred screening test for the hereditary red cell membrane disorders, because it binds band 3 and the Rh-related proteins whose reduced density is the common endpoint of the different molecular defects. The test is more sensitive and specific than the older osmotic fragility test, which is also raised after any recent transfusion. If the screen is positive, sodium dodecyl sulfate polyacrylamide gel electrophoresis of the red cell membrane proteins confirms the diagnosis and identifies the defective protein, which has implications for family counselling. ^[2]

Pathophysiology

Hereditary spherocytosis destabilises the vertical interactions between the membrane skeleton and the lipid bilayer, through defects in ankyrin, spectrin, band 3 or protein 4.2. The red cell loses surface area relative to its volume and becomes a small, dense, rigid spherocyte that cannot deform in the splenic microcirculation. The spleen traps and destroys the spherocytes, producing the chronic haemolysis, splenomegaly, raised reticulocyte count, low haptoglobin and raised unconjugated bilirubin. The raised mean corpuscular haemoglobin concentration reflects the dehydration and surface-area loss of the spherocyte. ^[1]