This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Anatomy
MCHC is increased in 
Select and explain. 
A. Iron deficiency anaemia, B. Spherocytosis, C. Thalassemia, D. All
B: Spherocytosis
Answer: B: Spherocytosis 
Explanation: Ref Robbins 9/e p633 MCHC can be elevated ("polychromatic") in hereditary spherocytosis, sickle cell disease and homozygous haemoglobin C disease, depending upon the hemocytometer. MCHCcan be elevated in some megaloblastic anemias. Spherocytosis most often refers to hereditary spherocytosis. This is caused by a molecular defect in one or more of the proteins of the red blood cell cytoskeleton, including spectrin, ankyrin, Band 3, or Protein 4.2. Because the cell skeleton has a defect, the blood cell contracts to a sphere, which is its most surface tension efficient and least flexible configuration. Though the spherocytes have a smaller surface area through which oxygen and carbon dioxide can be exchanged, they in themselves perform adequately to maintain healthy oxygen supplies. However, they have a high osmotic fragility--when placed into water, they are more likely to burst than normal red blood cells. These cells are more prone to physical degradation.