Why is MCV increased in folic acid deficiency but decreased in iron deficiency?

Answer:
Folic acid (like B12) is required for DNA synthesis and cell division. If you're low on folate, your blood cells can grow, but they can't divide. Hence, the mean cell volume (MCV) increases.Iron is a key component of hemoglobin, the main protein component of RBCs. Without iron, your blood cells can divide but not grow. Therefore, the MCV decreases.

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MCV relates to the size of red blood cells. RBC's start large and get broken down into their normal size. Folic acid plays a role in breaking it down. A deficiency reduces breakdown, so the existing cells are larger and the MCV is high.

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