Hereditary Spherocytosis (HS) is caused by defects of red cell membrane proteins (spectrin, ankyrin, band 3 and band 4.2). The aim of this study is to analyse a large database of 300 HS patients grouped according to SDS-PAGE, 1) to ascertain whether the clinical/haematological features and response to splenectomy are related to the type of molecular defect, and 2) to compare the sensitivity of the most common laboratory screening tests for HS in the various subsets of patients. Three hundred consecutive patients were investigated; 41 patients had been splenectomised before the time of the study, and 21 thereafter. In not splenectomised subjects, anaemia was severe in 7% of cases, mild to moderate in 52% and compensated in the remaining cases. The median number of spherocytes at the peripheral blood smear examination was 7%. The most frequent protein abnormalities revealed by SDS-PAGE were band 3 (54%) and spectrin and/or ankyrin (34%) deficiency. The membrane protein defect was undetectable in 3% of splenectomised versus 11% of not splenectomised patients. In patients evaluated by SDS-PAGE before and after splenectomy surgery allowed the identification of the defect (one band 3 and seven spectrin/ankyrin deficiency) in all the 8 previously unclassified cases. No significant differences were observed among clinical and haematological parameters of patients grouped according to the type of biochemical defect, although the degree of anaemia, haemolysis markers and median spherocyte number were higher in spectrin deficient than in the other groups of patients. Splenectomy was clinically effective in correcting both anaemia and haemolysis, but splenectomised spectrin/ankyrin deficient patients showed after splenectomy a slightly lower median rise in haemoglobin, and a higher reticulocyte number and unconjugated bilirubin level than band 3 deficient patients. The red cell osmotic fragility tests’ sensitivity varies greatly and ranged from 48 to 95%. The sensitivity was similar in patients with band 3 and spectrin/ankyrin deficiency and also in patients without detectable membrane defect. Furthermore, the sensitivity of all the methods investigated increased in splenectomised cases. AGLT displayed the highest sensitivity, and the association of AGLT and NaCl test on incubated blood reached a sensitivity of 99%, enabling the diagnosis of the atypical HS cases, such as those with rare or no spherocytes in blood smears, normal MCHC and reticulocyte counts.

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