Which diagnostic finding is characteristic of hereditary spherocytosis?

Which diagnostic finding is characteristic of hereditary spherocytosis?

• A. Osmotic fragility test positive
• B. Coombs test positive
• C. Increased mean corpuscular hemoglobin concentration
• D. Hypersegmented neutrophils

Answer: (A)

Defects in the red blood cell membrane skeleton (such as spectrin or ankyrin) cause the cells to lose membrane surface area and become small, spherical, and less deformable. This makes them particularly fragile in hypotonic environments and more likely to be destroyed by the spleen, leading to hemolytic anemia. The osmotic fragility test measures how easily red cells lyse as salt concentration becomes more hypotonic. In hereditary spherocytosis, the spherocytes have reduced surface area-to-volume ratio, so they rupture at higher, less hypotonic saline concentrations. This yields a positive osmotic fragility test, which is the characteristic diagnostic finding. Coombs (direct antiglobulin) would be negative because this is not an autoimmune process. Hypersegmented neutrophils point toward megaloblastic anemia, not hereditary spherocytosis. Increased mean corpuscular hemoglobin concentration can occur with HS due to red cell dehydration, but it is not as specific or definitive as the positive osmotic fragility test.

Defects in the red blood cell membrane skeleton (such as spectrin or ankyrin) cause the cells to lose membrane surface area and become small, spherical, and less deformable. This makes them particularly fragile in hypotonic environments and more likely to be destroyed by the spleen, leading to hemolytic anemia.

The osmotic fragility test measures how easily red cells lyse as salt concentration becomes more hypotonic. In hereditary spherocytosis, the spherocytes have reduced surface area-to-volume ratio, so they rupture at higher, less hypotonic saline concentrations. This yields a positive osmotic fragility test, which is the characteristic diagnostic finding.

Coombs (direct antiglobulin) would be negative because this is not an autoimmune process. Hypersegmented neutrophils point toward megaloblastic anemia, not hereditary spherocytosis. Increased mean corpuscular hemoglobin concentration can occur with HS due to red cell dehydration, but it is not as specific or definitive as the positive osmotic fragility test.