What it measures.
MCV (Mean Corpuscular Volume) measures the average volume of your red blood cells. Low MCV (microcytic) suggests iron deficiency or thalassemia; high MCV (macrocytic) points to B12 deficiency, folate deficiency, or liver disease. MCV helps identify the cause of anemia.
The average volume of individual red blood cells, measured in femtoliters (fL). Calculated from hematocrit and RBC count.
Why it matters.
MCV is the first clue to what's causing anemia. Small cells indicate problems with hemoglobin production (iron, thalassemia); large cells indicate problems with DNA synthesis (B12, folate). This guides further testing and treatment.
Physiology.
Red blood cell size reflects how they were produced in bone marrow. Iron deficiency reduces hemoglobin content, causing cells to be smaller. B12/folate deficiency impairs DNA synthesis, causing cells to divide less frequently and grow larger before release.
Testing & preparation.
How to prepare
- No special preparation needed
- Part of standard CBC
When to test
When anemia is found, to help classify the type and guide further workup.
How often
With each CBC; as needed when monitoring anemia treatment.
Interpretation.
High mcv
Common causes:
- B12 deficiency
- Folate deficiency
- Alcohol use
- Liver disease
- Hypothyroidism
- Myelodysplastic syndromes
- Certain medications (methotrexate)
- Reticulocytosis (young RBCs are larger)
Implications:
- MCV >100 fL: macrocytic anemia
- MCV >120 fL: highly likely B12 or folate deficiency
- Check B12, folate, and liver function
- May cause neurological symptoms if B12-related
Low mcv
Common causes:
- Iron deficiency (most common)
- Thalassemia trait
- Chronic disease anemia
- Lead poisoning
- Sideroblastic anemia
Implications:
- MCV <80 fL: microcytic anemia
- Check iron studies (ferritin, TIBC)
- If iron normal, consider thalassemia screening
- May indicate chronic blood loss
Optimization.
Diet
- Iron-rich foods for microcytic pattern
- B12-rich foods for macrocytic pattern
- Folate from leafy greens
Lifestyle
- Limit alcohol if macrocytic
- Identify and address underlying cause
Supplements
- Iron for iron deficiency microcytosis
- B12 for macrocytic anemia
- Folate if deficient
FAQs.
What if my MCV is normal but I'm still anemic?
Normal MCV (normocytic) anemia has different causes: chronic disease (inflammation, infection, cancer), acute blood loss, early iron deficiency (before MCV falls), kidney disease (reduced EPO), or mixed deficiencies (iron + B12 averaging to normal MCV). Check RDW—if elevated with normal MCV, it suggests mixed deficiency where small and large cells are averaging out.
Can MCV be normal in iron deficiency?
Yes, especially in early iron deficiency. MCV falls relatively late in the progression. Ferritin drops first, then serum iron, then hemoglobin, and finally MCV. You can have iron deficiency with fatigue and low ferritin while MCV is still normal. This is why ferritin is important even when CBC looks normal.