Hereditary spherocytosis is caused by defects in proteins of the red blood cell membrane skeleton (like ankyrin, band 3, or spectrin). This leads to loss of membrane stability and surface area. The red cells become spherical (spherocytes) instead of the normal biconcave disc shape. On a peripheral blood smear, these spherocytes appear as small, round, densely staining red cells that lack the central area of pallor. They are less deformable and are trapped and destroyed in the spleen, leading to extravascular hemolysis. Other lab features include increased MCHC (because the cell loses membrane but not volume, concentrating the hemoglobin), increased osmotic fragility (these spherical cells burst more easily in hypotonic solutions), reticulocytosis, and elevated bilirubin. A positive DAT is not a feature; that is seen in immune hemolytic anemias.

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Zambia

• loveness Phiri – 801 pts

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