Which laboratory finding is most characteristic of vitamin B12 deficiency?

Which laboratory finding is most characteristic of vitamin B12 deficiency?

• A. Normal MCV
• B. Macrocytic anemia with hypersegmented neutrophils
• C. Microcytic anemia
• D. Elevated reticulocytes

Answer: (B)

Impaired DNA synthesis in hematopoietic cells leads to megaloblastic changes, so developing red cells mature abnormally. This produces a macrocytic anemia with a high mean corpuscular volume, and on the peripheral smear you see hypersegmented neutrophils, reflecting delayed nuclear maturation. That combination—macrocytic anemia with hypersegmented neutrophils—is the classic laboratory signature of vitamin B12 deficiency. Normal MCV is not typical because the RBCs are enlarged; a microcytic pattern points to iron deficiency or other causes of small cells; an elevated reticulocyte count suggests active production or hemolysis, which isn’t the issue in B12 deficiency.

Impaired DNA synthesis in hematopoietic cells leads to megaloblastic changes, so developing red cells mature abnormally. This produces a macrocytic anemia with a high mean corpuscular volume, and on the peripheral smear you see hypersegmented neutrophils, reflecting delayed nuclear maturation. That combination—macrocytic anemia with hypersegmented neutrophils—is the classic laboratory signature of vitamin B12 deficiency.

Normal MCV is not typical because the RBCs are enlarged; a microcytic pattern points to iron deficiency or other causes of small cells; an elevated reticulocyte count suggests active production or hemolysis, which isn’t the issue in B12 deficiency.