The MCV blood test measures the Mean Corpuscular Volume, which is a value that indicates the average size of red blood cells. It is usually a part of the complete blood count.
A high or low MCV result can be a sign of anemia, bleeding, hypothyroidism, thalassemia or chronic infections, for example.
Knowing the MCV is particularly important for helping to diagnose anemia and to monitor the patient after starting anemia treatment. However, the MCV result should be interpreted alongside the entire blood count (especially the MCV, RDW and hemoglobin) and not in isolation.
Normal levels
The normal value for MCV is between 80 and 100 fl, although these values may vary depending on the laboratory.
Abnormal levels
MCV can be abnoral for the following reasons:
High MCV
A high MCV indicates that the red blood cells are larger than normal, which can be a sign of:
- Megaloblastic anemia
- Pernicious anemia
- Alcohol dependence
- Bleeding
- Myelodysplastic syndrome
- Hypothyroidism
A high MCV may also present with a high RDW, which is a value that assesses the difference in size between red blood cells.
Low MCV
A low MCV indicates that the red blood cells present in the blood are small, known or microcytic:
- Iron deficiency anemia
- Thalassemia minor
- Congenital spherocytosis
- Uremia
- Chronic infections
A low MCV caused by iron deficiency anemia may also cause an abnormal MCH, which assesses the concentration of hemoglobin per red blood cell. Read more about the MCH blood test.
MCV and anemia
To diagnose anemia, the doctor will typically check hemoglobin levels, as well as other red blood cell characteristics reported in the MCV and MCH tests. Anemia types can be identified as follows:
- Low hemoglobin + low MCV and MCH: This suggests a microcytic anemia, such as iron deficiency anemia;
- Low hemoglobin + normal MCV and MCH: This suggests normocytic anemia, and may be indicative of thalassemia;
- Low hemoglobin + high MCV: This suggests macrocytic anemia, such as megaloblastic anemia.
Based on the full results of the complete blood count, the doctor may order other tests that can confirm the diagnosis of anemia. Learn more about the anemia blood tests your doctor may order.