The size of many of these RBC's is quite small, with lack of the central zone of pallor. These RBC's are spherocytes. In hereditary spherocytosis, there is an abnormality of RBC cytokeletal membrane proteins such as ankyrin and spectrin. This produces membrane instability that forces the cell to the smallest volume--a sphere. In the laboratory, this is shown by increased osmotic fragility. The spherocytes do not survive as long as normal RBC's.

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