Which statement correctly defines macrocytosis?

• A. Macrocytic corresponds to a size greater than 100 fL
• B. Macrocytic corresponds to a size less than 80 fL
• C. Macrocytic corresponds to a size 60-80 fL
• D. Macrocytic corresponds to a size 80-100 fL

Answer: (A)

Macrocytosis means red blood cells are larger than normal, which is reflected in the mean corpuscular volume (MCV) measured in femtoliters. The normal MCV range is roughly 80–100 fL; when MCV exceeds 100 fL, the cells are considered macrocytic. This is why the statement describing macrocytosis as a size greater than 100 fL is the correct definition. In contrast, an MCV below 80 fL indicates microcytosis, and an MCV in the 80–100 fL range is normocytic. Macrocytosis can arise from conditions that enlarge RBCs or delay nuclear maturation, such as reticulocytosis or B12/folate deficiency, and recognizing the size criterion helps guide subsequent evaluation.