<prompt> Not a feature of hereditary Spherocytosis: March 2007Autosomal dominantIncreased RBC surface areaIncreased MCHCNormal or decreased MCV  <response>: Ans. B: Increased RBC surface area Its the only condition presenting with Increased MCHC Spherocytosis is caused by a molecular defect in one or more of the proteins of the red blood cell cytoskeleton, including, spectrin, ankyrin so blood cell contracts to its most surface-tension efficient and least flexible configuration, a sphere spherocytes. They have a high osmotic fragility and are more prone to physical degradation. They are most commonly found in immunologically-mediated hemolytic anemias and in hereditary spherocytosis, but the former would have a positive direct Coombs test and the latter would not. The misshapen but otherwise healthy red blood cells are mistaken by the spleen for old or damaged red blood cells and it thus constantly breaks them down, causing a cycle whereby the body destroys its own blood supply auto-hemolysis. Chronic symptoms include anemia and splenomegaly. As a result of the broken-down blood cells -- bilirubin -- accumulates in the gallbladder and can cause pigmented gallstones to develop. In peripheral blood smears, red blood cells will appear abnormally small. The CBC will show elevated MCHC. The bone marrow in its role of manufacturing red blood cells will display hyperplasia, the increased activity of replacing RBCs. As a result, immature red blood cell or reticulocyte counts will appear elevated. 