Which peripheral smear finding is characteristic of vitamin B12 deficiency?

Which peripheral smear finding is characteristic of vitamin B12 deficiency?

• A. Hypersegmented polymorphonuclear WBCs
• B. Target cells
• C. Sideroblastic anemia
• D. Howell-Jolly bodies

Answer: (A)

Hypersegmented neutrophils on the peripheral smear are a classic finding in megaloblastic anemia caused by vitamin B12 deficiency. When B12 is deficient, DNA synthesis in hematopoietic cells slows, so cell maturation lags behind cytoplasmic development. This mismatch leads to delayed nuclear division and cells with nuclei that have more lobes than normal. In circulating white cells, this shows up as neutrophils with multiple (often >5) nuclear lobes, the hallmark smear feature. You’ll commonly see these alongside macrocytosis and oval macrocytes in red cells, reflecting the overall enlarged cell size. Other options point to different conditions: target cells are typically seen with liver disease, thalassemias, or hemoglobinopathies; sideroblastic anemia involves defective heme synthesis and ring sideroblasts; Howell-Jolly bodies indicate splenic dysfunction or loss. But the distinctive smear finding that ties directly to vitamin B12–related megaloblastic anemia is hypersegmented neutrophils.

Hypersegmented neutrophils on the peripheral smear are a classic finding in megaloblastic anemia caused by vitamin B12 deficiency. When B12 is deficient, DNA synthesis in hematopoietic cells slows, so cell maturation lags behind cytoplasmic development. This mismatch leads to delayed nuclear division and cells with nuclei that have more lobes than normal. In circulating white cells, this shows up as neutrophils with multiple (often >5) nuclear lobes, the hallmark smear feature. You’ll commonly see these alongside macrocytosis and oval macrocytes in red cells, reflecting the overall enlarged cell size.

Other options point to different conditions: target cells are typically seen with liver disease, thalassemias, or hemoglobinopathies; sideroblastic anemia involves defective heme synthesis and ring sideroblasts; Howell-Jolly bodies indicate splenic dysfunction or loss. But the distinctive smear finding that ties directly to vitamin B12–related megaloblastic anemia is hypersegmented neutrophils.