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Answer = Osmotic gradient ektacytometry measures RBC deformability under a defined shear stress as a function of suspending medium osmolality. The test is used to evaluate for inherited RBC membrane disorders, which are commonly responsible for hemolytic anemia, differentiating among hereditary spherocytosis (HS), hereditary elliptocytosis (HE) and pyropoikilocytosis (HPP), Southeast Asian ovalocytosis (SAO) and hereditary stomatocytosis (HSt).
Three distinct features of the osmotic gradient ektacytometry profiles are:
 Omin: Corresponds to the value of the hypotonic osmolality where 50 percent of the cells hemolyze in an osmotic fragility assay and provides information on the initial surface-to-volume ratio of the cell sample.
 EImax: Elongation index reaches a maximum near 300 mOsm/kg, suggesting that the normal red cell deforms optimally at the tonicity to which it is normally exposed. The value of EImax depends mostly on the cytoskeleton mechanics.
 Ohyp: The declining portion of the curve (the osmolality value where the cells are at half of the maximum elongation) correlates with the initial MCHC (intracellular viscosity) of the cell sample.
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