In-depth analysis of osmotic gradient ektacytometry parameters across different genotypes in hereditary spherocytosis

Hereditary spherocytosis (HS) is a hereditary haemolytic anaemia, caused by pathogenic variants in genes encoding red blood cell membrane proteins. Osmotic gradient ektacytometry evaluates red cell deformability and hydration and is increasingly used in the diagnosis of HS. We retrospectively evaluated laboratory data from 233 HS patients focusing on osmotic gradient ektacytometry parameters, including two novel parameters, O_min-width and O_max-width. We found that the maximum elongation index (EI_max), representing the maximum deformability, was decreased in SPTB relative to SLC4A1 and SPTA1 (0.509 vs. 0.557 and 0.564, both p < 0.01). Hydration was most affected in SLC4A1, with the lowest median O_hyper (416 mOsm/kg). The novel parameters also showed differences: O_min-width was higher in SPTB and ANK1 compared to SLC4A1 and SPTA1 (p < 0.05). O_max-width was lowest in SLC4A1 (92 mOsm/kg). We found that non-missense variants, opposed to missense variants, were associated with decreased deformability in SPTB and ANK1 subgroups as well as with decreased hydration in the ANK1 subgroup specifically (O_hyper missense 472 mOsm/kg vs. non-missense 436 mOsm/kg). Lastly, when classifying disease severity based on reticulocyte production index, we found that O_min, EI_max, area under the curve (AUC), O_min-width and O_max-width differed between mild and moderate patients (all p < 0.05). Our findings suggest that osmotic gradient ektacytometry provides additional information on HS pathophysiology and clinical severity.