What Is a Mean Corpuscular Volume (MCV) Test?

A mean corpuscular volume (MCV) test is a blood test that measures the size and volume of your red blood cells. Red blood cells help carry oxygen from the lungs to other body parts. An MCV test is often part of a routine blood test called a complete blood count (CBC).

An MCV test can help diagnose several conditions, especially anemia—when your body doesn't have enough healthy red blood cells. A low MCV means your red blood cells are smaller than normal, while a high MCV means your red blood cells are larger than normal. The abnormality in red blood cell size that MCV shows can help determine which type of anemia you have and may also help identify other conditions, such as liver disease.

Purpose

An MCV test is typically part of a complete blood count (CBC). A CBC is a common blood test that measures different components of your blood, including:

• Red blood cells
• White blood cells
• Hemoglobin, a protein in red blood cells that carries oxygen
• Platelets, which help with blood clotting

A CBC is often ordered to check general health. Its results can help diagnose and monitor several health conditions, including infections, anemia, blood cancers, and immune-related conditions.

An MCV test measures the average size and volume of red blood cells. This helps determine which type of anemia you have and its underlying cause. The test can also detect other conditions such as colorectal cancer, esophageal cancer, chronic kidney disease, and ischemic stroke (when a blood clot blocks or plugs an artery to your brain).

Your healthcare provider may recommend an MCV test if you are experiencing symptoms like:

• Weakness
• Shortness of breath
• Fatigue
• Dizziness
• Headache
• Abnormal heart rhythm

How Does It Work?

The MCV test is done by drawing blood from a vein in your arm—a process called venipuncture. The blood sample collection usually takes place at the healthcare provider’s office or a clinical laboratory. There is not typically anything special you need to do before or after the test.

Before the Test

An MCV test is part of a routine CBC, and a CBC doesn't require any special preparation. You'll want to stay hydrated so the phlebotomist (a medical professional trained to draw blood) can more easily find a vein.

You don't need to fast (refrain from eating or drinking) for a CBC. However, you might receive other tests on the same day that require fasting for a certain amount of time beforehand. You might also need to stop certain medications or supplements before testing. Your healthcare provider will let you know.

Once in the testing room, you will be asked to sit in a comfortable chair. You may be asked to lie down if you have a previous history of fainting or panic attacks during blood tests.

During the Test

During the MCV test, the phlebotomist draws blood from a vein in your arm using a small needle. The blood drawing process involves the following steps:

• Cleaning the area with an antiseptic solution
• Putting an elastic band around your upper arm to put pressure on the area
• Inserting a needle into the vein and collecting blood in an airtight vial or tube attached to the needle
• Removing the needle and band from your arm
• Putting a cotton pad or bandage on the needle site

You may feel slight pain or a stinging sensation at the needle site. However, such symptoms should go away quickly.

The blood draw usually takes no more than five minutes.

After the Test

Your healthcare provider may ask you to stay in the office for a few minutes if you experience dizziness or weakness after the test. Otherwise, as long as you feel up to it, you can resume most of your daily activities virtually immediately after the test.

You may be advised to avoid lifting heavy objects for up to 24 hours after the test as doing so can cause bruising and bleeding at the needle site.

Risks and Precautions

Like all blood tests, MCV tests are relatively safe with low risk. However, some people may experience certain complications such as:

• Pain in and around the needle site
• Slight bruising at and around the needle site
• Abnormal clotting of blood
• Infection at the needle site
• Nerve damage

How To Prepare for an MCV Test

An MCV test is quite straightforward, but you can talk to your healthcare provider about concerns or ask questions about the process. Here are a few things to consider:

• Location: The test might take place at the healthcare provider’s office or clinic. It might also take place at a hospital or diagnostic center where a phlebotomist takes the blood.
• Attire: You may want to wear short sleeves so it's easier to expose arm veins. If you wear a long-sleeved shirt, make sure you can easily push up the sleeve.
• Food and drink: Ask your healthcare provider about any restrictions regarding food or beverages leading up to the test.
• Medications: Certain medications or nutritional supplements can interfere with test results. Ask your healthcare provider if you should discontinue them before the test and, if so, for how long before.
• Emotional support: You can bring someone for the test if you feel anxious.
• Cost and insurance: You can call or message your insurance provider to see if they will cover some or all test costs.

Results

The results of an MCV test are usually ready within a few hours to a few days, depending on the lab. Some labs have an online patient portal for you to check the results yourself. The healthcare provider who ordered the test may call you with the results.

Depending on the results, you may need to visit your healthcare provider to discuss the findings and determine whether you need further testing.

Interpreting Results

Your MCV is calculated by using a formula: hematocrit (percentage of red blood cells in your blood) multiplied by 10 and divided by your red blood cell count:

• 80-100 femtoliters (fL): Your red blood cells are a normal size.
• Less than 80 fL: Your red blood cells are smaller than normal.
• More than 100 fL: Your red blood cells are larger than normal.

MCV values vary with age. MCV is generally slightly higher in people assigned female at birth until people reach 30 years old. After this, MCV generally becomes higher in people assigned male at birth.

Low MCV

Low MCV suggests you have microcytic anemia, which is when red blood cells are smaller than they should be. You may also have low MCV levels due to:

• Iron deficiency anemia: A lack of healthy red blood cells due to low iron levels
• Thalassemia: An inherited blood disorder caused by low hemoglobin (a protein)
• Anemia of chronic disease: Anemia that affects people with inflammatory conditions
• Sideroblastic anemia: Anemia caused by the misuse of iron during the creation of red blood cells

High MCV

High MCV suggests you have macrocytic anemia. Macrocytic anemia can develop because your body doesn't have the proper nutrients to form enough red blood cells.

You may also have high MCV levels due to:

• Vitamin B12 deficiency
• Vitamin B9 (folate) deficiency
• Liver disease
• Hyperglycemia (high blood sugar)
• Thyroid dysfunction
• Excessive alcohol consumption
• Multiple myeloma (a type of blood cancer)
• Down syndrome
• Hemolytic anemia (when your red blood cells are destroyed faster than they can be replaced)

Normal MCV

You can have anemia even if your MCV levels are normal. This type of anemia is called normocytic anemia. It most often occurs due to impaired red blood cell production. MCV might also be normal with:

• Excessive blood loss
• Hemolytic anemia
• Chronic kidney disease
• Thyroid disorder
• Anemia of chronic disease

If your MCV is normal but anemia is suspected, a healthcare provider can look at the results of other blood tests or run additional tests to make a diagnosis.

A Quick Review

The mean corpuscular volume (MCV) test is a blood test that's usually done as part of a complete blood count (CBC). An MCV test helps measure the average size and volume of red blood cells. It's especially helpful in diagnosing anemia.

Your results—high, low, or normal MCV—can reveal your specific type of anemia. Your healthcare provider may also recommend other tests to help diagnose anemia and other conditions.