What RBC morphology is characteristic of megaloblastic anemia due to folic acid or vitamin B12 deficiency?

• A. Microcytosis
• B. Macrocytosis
• C. Spherocytosis
• D. Elliptocytosis

Answer: (B)

Megaloblastic anemia from folate or B12 deficiency causes impaired DNA synthesis, so red blood cell precursors in the bone marrow don’t divide normally and become oversized. That leads to macrocytosis, with circulating red cells that are larger than normal (macrocytes) and often oval-shaped. This macrocytic picture is typical, whereas microcytosis would point to iron deficiency or thalassemia, and spherocytosis or elliptocytosis relate to membrane disorders, not the megaloblastic process. So the characteristic RBC morphology is macrocytosis.