Pancytopenia with hypersegmented neutrophils and an abnormal Schilling test is characteristic of which anemia?

• A. Pernicious anemia
• B. Folate deficiency anemia
• C. Aplastic anemia
• D. Iron deficiency anemia

Answer: (A)

This scenario reflects a failure of vitamin B12–dependent DNA synthesis, which drives megaloblastic changes in the bone marrow. When B12 is deficient, hematopoietic cells can’t synthesize DNA properly, leading to large, immature cells and hypersegmented neutrophils. Pancytopenia arises from ineffective hematopoiesis affecting all lineages. The Schilling test measures how well vitamin B12 is absorbed in the gut; an abnormal result points to B12 malabsorption, most classically from pernicious anemia, where autoimmune destruction of intrinsic factor or gastric parietal cells impairs B12 uptake.

Folate deficiency can also cause hypersegmented neutrophils and pancytopenia, since it, too, disrupts DNA synthesis, but the Schilling test would be normal because B12 absorption is unaffected. Aplastic anemia shows pancytopenia with a hypocellular marrow and does not feature hypersegmented neutrophils or rely on a Schilling test. Iron deficiency anemia typically causes microcytic changes rather than macrocytosis or hypersegmentation and is unrelated to B12 absorption testing.