May‐Jean King

Guidelines on hereditary spherocytosis (HS) published in 2004 (Bolton-Maggs et al, 2004) are here replaced to reflect changes in current opinion on the surgical management, (particularly the indications for concomitant splenectomy with cholecystectomy in children with mild HS, and concomitant cholecystectomy with splenectomy in those with asymptomatic gallstones). Further potential long term hazards of splenectomy are now recognised. Advances have been made in our understanding of the biochemistry of the red cell membrane which underpins the choice of tests. Biochemical assays of membranes proteins and genetic analysis may be indicated (rarely) to diagnose atypical cases. The diagnostic value of the eosin-5-maleimide (EMA) binding test has been validated in a number of studies with understanding of its limitations.

The flow cytometric test measures the fluorescence intensity of intact red cells labelled with the dye eosin-5-maleimide, which reacts covalently with Lys-430 on the first extracellular loop of band 3 protein. In this study, red cells from patients with hereditary spherocytosis (HS), congenital dyserythropoietic anaemia type II, South-east Asian ovalocytosis and cryohydrocytosis have produced a greater degree of reduction of mean channel fluorescence readings than those for other patient groups and normal controls. The predictive value of this test for membrane abnormality was compared with the results obtained from the sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) method, which is currently the reference laboratory test for the identification of membrane protein deficiencies in hereditary spherocytosis and for the detection of spectrin variants in hereditary elliptocytosis. The dye method is a reliable, speedy diagnostic test (2 h from sample collection to result) for HS with a sensitivity of 92.7% and a specificity of 99.1%. Thus, it will serve well as a first-line screening test for the diagnosis of hereditary spherocytosis in routine haematology.

Flow cytometric analysis of eosin-5-maleimide (EMA) binding to red cells is a screening test for the diagnosis of hereditary spherocytosis (HS). The present study used chemical modifications to determine the integral membrane proteins that react with EMA. The predominant interaction of EMA, contributing c. 80% of fluorescence, was with the epsilon-NH2 group of lysine in band 3 protein, as previously reported. The remainder of the EMA fluorescence was attributable to labelling of accessible sulfhydryl groups on intact red cells. This reaction was heat labile. Three molecules containing sulfhydryl groups were shown to be associated with the Rh blood group protein complex by sodium dodecyl sulphate polyacrylamide gel electrophoresis. These were CD47 and the Rh-associated glycoprotein, both in the Mr 40-60 kD region, and the Rh blood group proteins in the 30-32 kD region. Immunoprecipitation, using specific monoclonal antibodies and antibody binding studies by flow cytometry, showed that the relative content of these three membrane proteins was lower in HS than normal red cells. Thus, the high predictive value of the EMA binding test for HS reflects changes in the relative amounts of the Rh-related integral membrane proteins as well as band 3 in HS red cells.

BACKGROUND: Flow cytometric analysis of eosin-5-maleimide (EMA)-labeled red blood cells (RBCs) has been used as a screening test for the diagnosis of patients with hereditary spherocytosis (HS). We assessed the fluorescence profiles for patients having HS and hereditary pyropoikilocytosis (HPP) together with their red cell indices. METHODS: Flow cytometry was used to analyze EMA-labeled RBCs. Membrane protein defects and spectrin variants were identified by SDS-polyacrylamide gel electrophoresis. RESULTS: An overlay of single fluorescence peaks for normal individuals, and those with HS and HPP revealed a graded fluorescence intensity (normal > HS > HPP). The area under each peak defined a specific RBC subpopulation; namely, normal RBCs, spherocytes, and microspherocytes. HS RBCs having a gross reduction in band 3 or spectrin content gave fluorescence readings almost as low as those for HPP. Complex fluorescence profiles were obtained for isolated HS and HPP cases. CONCLUSIONS: The mean cell volume is a useful discriminator for HS and HPP. We presented evidence that a mixed RBC population could occur in some HS and HPP patients, either in a transient manner or for a long-term period. A differential diagnostic scheme for detecting HPP and HS by flow cytometry is proposed.