Mean corpuscular volume (MCV)

What it measures

The average size of red cells. It is the main index for sorting anemia into microcytic, normocytic or macrocytic types, which guides further testing.

Specimen and preparation

• Specimen: Whole blood (EDTA)
• Tube: Lavender top
• Preparation: Test within 24 h; stored samples show cell swelling and a falsely high MCV.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Vitamin B12 or folate deficiency
• Alcohol use and liver disease
• Hypothyroidism
• Reticulocytosis
• Drugs (methotrexate, hydroxyurea, zidovudine)
• Myelodysplastic syndrome

Causes of low values

• Iron deficiency
• Thalassemia trait or disease
• Anemia of chronic disease (some cases)
• Sideroblastic anemia
• Lead poisoning

Method

Direct measurement by analyzer, or calculated as Hct/RBC × 10

Good to know

A mixed deficiency (iron plus B12) can give a normal MCV; check RDW and the blood film. Cold agglutinins falsely raise MCV.

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