<prompt> Which is the most common red cell defect without Hb abnormality?ElliptocytosisSpherocytosisPoikilocytosisSickle cell disease  <response>: Anisocytosis: Variation in size seen in thalassemia which is a hemoglobin abnormalityPoikilocytosis: Variation in shape seen in thalassemia which is a hemoglobin abnormalityElliptocytosis: A red cell membrane disorder without Hb abnormality, but not so commonSickle cell anemia: A qualitative Hb disorder Spherocytosis: Spherocytosis occurs due to membrane defect which could be hereditary or due to autoimmune hemolytic anemia. The condition has no relation to hemoglobin. If all causes of spherocytosis are taken into account, it is the most common red cell defect compared to other options. Ref: Robbins 8e p650 