Distinguishing features between hereditary spherocytosis (HS) and hereditary elliptocytosis (HE) on the blood smear, ektacytometry, and EMA binding

RBCs from patients with HS and HE have different properties that can be distinguished using specialized laboratory tests. Ektacytometry (eg, Osmoscan) measures the deformability (deformability index on the Y-axis) across a gradient of osmolalities (on the X-axis). EMA binding measures the band 3 content of RBCs, with the control in white and the patient samples in red (pink is the region of overlap).
(A) HS. All measures of deformability (all parts of the tracing on ektacytometry) are below the values for normal RBCs, consistent with a decrease in RBC minimal and maximal deformability. The minimal deformability index on the left of the scan is the osmolality where hemolysis occurs and is shifted to the right in HS. EMA binding is shifted to the left due to reduced band 3 content.
(B) HE. The peak deformability (peak of the ektacytometry graph) is lower, consistent with lower maximal flexibility and decreased deformability under shear stress, but the outer edges of the peak (including Omin, the osmolality at which 50% of RBC lyse) are relatively normal, consistent with less severe (or no) hemolysis in most cases. Band 3 content is slightly increased in full elliptocytes and much lower in elliptocyte fragments from a severe HE patient.