Which peripheral blood finding is characteristic of vitamin B12 deficiency causing macrocytic anemia?

Which peripheral blood finding is characteristic of vitamin B12 deficiency causing macrocytic anemia?

• A. Hyposegmentation of neutrophils
• B. No abnormalities in neutrophils
• C. Megakaryocytosis in marrow
• D. Hypersegmented neutrophils

Answer: (D)

Vitamin B12 deficiency disrupts DNA synthesis, leading to megaloblastic maturation and delayed nuclear development in hematopoietic cells. On the peripheral blood smear, neutrophils show nuclei with an excessive number of lobes, known as hypersegmented neutrophils. This finding is a classic clue to megaloblastic anemia from B12 (or folate) deficiency and accompanies the macrocytosis seen in these patients. Other choices don’t fit as well because hyposegmentation of neutrophils suggests other conditions (like Pelger-Huët anomaly or related disorders) and is not typical of B12 deficiency; absence of neutrophil abnormalities would miss the hallmark; and megakaryocytosis refers to a marrow finding rather than a peripheral blood feature.

Vitamin B12 deficiency disrupts DNA synthesis, leading to megaloblastic maturation and delayed nuclear development in hematopoietic cells. On the peripheral blood smear, neutrophils show nuclei with an excessive number of lobes, known as hypersegmented neutrophils. This finding is a classic clue to megaloblastic anemia from B12 (or folate) deficiency and accompanies the macrocytosis seen in these patients.

Other choices don’t fit as well because hyposegmentation of neutrophils suggests other conditions (like Pelger-Huët anomaly or related disorders) and is not typical of B12 deficiency; absence of neutrophil abnormalities would miss the hallmark; and megakaryocytosis refers to a marrow finding rather than a peripheral blood feature.