Which condition is commonly associated with macrocytic anemia?

• A. B12 deficiency
• B. Iron deficiency
• C. Acute blood loss
• D. Hypothyroidism

Answer: (A)

Macrocytic anemia means the red blood cells are larger than normal (increased MCV). A classic and most common cause is vitamin B12 deficiency. Without enough B12, DNA synthesis in developing erythroid cells slows, so nuclei fail to mature in step with the cytoplasm. This produces megaloblastic precursors and macrocytosis, often visible as macro-ovalocytes on a blood smear. Clinically, B12 deficiency can also cause neurologic symptoms due to demyelination, reinforcing its distinct role.

Iron deficiency, by contrast, typically yields microcytic, hypochromic cells; acute blood loss usually presents as normocytic anemia initially; hypothyroidism can be associated with macrocytosis but is less typical and less specific than B12 deficiency.