Increased osmotic fragility and ektacytometry. (A) Osmotic fragility curves indicate increased osmotic fragility in α-adducin–null RBCs. (B) The maximum value of the deformability index, DI_max, at 250 dynes/cm² is a direct measure of the mean RBC membrane surface area and is significantly reduced (P < .001) in α-adducin–null RBCs, confirming loss of membrane surface area (X ± SE). +/+ indicates wild-type; +/−, heterozygotes; and −/−, homozygous null.