MCV Blood Test

What is mean corpuscular volume (MCV)?

Mean corpuscular volume (MCV) is a value calculated during a routine blood test called a complete blood count (CBC). MCV measures the average size of your red blood cells. Your red blood cells carry oxygen throughout your body. This oxygen, in turn, powers your cells. The characteristics of your red blood cells — including size — provide information about how successfully they can transport oxygen.

An MCV blood test is helpful because having a large number of atypically large or atypically small red blood cells can indicate certain conditions. It’s less helpful if you have a wide variety of red blood cell sizes in a blood sample. In that case, even if there’s an abnormality, the numbers may average out as normal.

An MCV is routinely performed by an automated machine on all CBCs. It’s included on the portion of the CBC that provides information on your red blood cells in particular, called the RBC (red blood cell) indices.

RBC indices include the following measurements:

• Mean corpuscular volume (MCV): The average size of your red blood cells.
• Mean corpuscular hemoglobin (MCH): The average amount of hemoglobin in your red blood cells. Hemoglobin is an important protein that allows red blood cells to carry oxygen.
• Mean corpuscular hemoglobin concentration (MCHC): The average amount of hemoglobin concentration in your red blood cells.
• Red cell distribution width (RDW): How varied in size your red blood cells are.

An MCV alone doesn’t provide enough information for a diagnosis. When considered alongside these other tests, an MCV blood test can help your provider learn more about the health of your red blood cells and diagnose conditions.

When is an MCV blood test performed?

An MCV blood test is routinely performed during a CBC.

Changes in the MCV may be secondary to a number of conditions. For example, the MCV is low in iron deficiency anemia. In that case, you may need additional tests for iron deficiency.

The MCV may also change in conditions such as liver disease or deficiency of vitamin B12 or folate.

How does an MCV blood test work?

The test involves a healthcare provider taking a blood sample from your arm and sending it to a lab for analysis. A different provider will look at the blood sample underneath a microscope and record information about your blood cells, including the average size of your red blood cells.

How do I prepare for the test?

An MCV is a value calculated by an automated blood counter that’s based on the number of red blood cells in a volume of blood. It’s part of a routine CBC and doesn’t require any special preparation.

What should I expect during the test?

You’ll be seated for the blood draw. A healthcare provider will clean the injection site on your arm with an alcohol wipe. They’ll tie a rubber band above the site to restrict the blood flow so it’s easier to see your vein. You’ll feel a quick prick when the needle goes in. Blood will flow quickly into a vial. Once there’s enough blood, the provider will remove the needle.

The procedure takes fewer than five minutes.

What should I expect after the test?

The provider will apply a cotton ball and bandage on the injection site to stop any bleeding. You should be able to leave immediately unless you’re experiencing symptoms like light-headedness. In that case, the provider will monitor you until it’s safe for you to leave.

What are the risks of this test?

MCV blood tests aren’t considered risky. You may feel soreness in your arm where the needle went in, and you may notice some slight bruising, but these symptoms usually resolve quickly.

When should I know the results of an MCV blood test?

Complete blood count (CBC) results, which include the MCV, should be available on the same day as the blood draw. Ask how the results will be communicated to you (phone call, letter, online portal) and when you should expect them.

What type of results do you get and what do the results mean?

You’ll get a number that tells you the average size of your red blood cells and a range showing what’s considered normal. You can see if your number falls within the normal range. A normal MCV blood test value ranges from 80 femtoliters (fl) to 100 fl.

What level of MCV is concerning?

Low or high MCV may signal certain conditions. Still, you shouldn’t be concerned over MCV results alone. Your provider will consider MCV results alongside other test results, as well as your symptoms, to assess your health.

Low MCV

Low MCV (microcytosis) is less than 80 fl. It may be a sign of:

• Iron-deficiency anemia.
• Thalassemia.
• Other hemoglobin disorders.

High MCV

High MCV (macrocytosis) is greater than 100 fl. It may be a sign of:

• Pernicious anemia.
• Vitamin B12 deficiency.
• Folate deficiency.
• Liver disease.
• Bone marrow dysfunction, as in myelodysplastic syndrome.

Chemotherapy treatments may also cause you to have elevated MCV.

A note from Cleveland Clinic

An abnormal MCV doesn’t provide enough information about your red blood cells for your provider to diagnose a condition. So, you shouldn’t be too concerned if your MCV blood test number falls outside the normal range. Still, along with other tests in the RBC indices, an MCV blood test can help create a more comprehensive picture of how your red blood cells are working.