Normal range: Starts 0.48-ends 0.42 gm NaCl
Comment: Increased in almost all cases of hereditary spheroccytosis, acquired hemolytic diseases of the newborns. Resistance to osmotic lysis i.e low osmotic fragility characteristic of b-thalassemia. Also in iron deficiency, sickle cell anemia, sideroblastic anemia
Sample: Heparinized whole blood