Mean corpuscular volume (MCV), also known as mean cell volume, is an important number that appears on a complete blood count (CBC). MCV is a value that describes the average size of red blood cells in a blood sample. It can help diagnose various types of anemia and other health conditions.

While MCV can provide important information, it is not used on its own. The MCV is tested in conjunction with a blood test and other red blood cell measurements , including mean corpuscular hemoglobin concentration (MCHC) and red blood cell distribution width (RDW). Together they can be used to clarify the diagnosis.

A low MCV (called microcytosis ) means that the red blood cells are small (RBC). A high MCV ( macrocytosis ) means that the red blood cells are large.

MCV can be a useful test even if the red blood cell count and other tests are normal. This is especially true for kidney disease.

This article explains why the MCV test is performed, what to expect from the test, and how to interpret the results.

Purpose of the MCV test

MCV is one of the numbers provided as part of the CBC . In this way, healthcare providers see the MCV each time they request a CBC.

This type of blood test may be ordered as part of routine screening tests. It can also be done as part of the diagnosis, treatment, and follow-up of many diseases.

However, there are times when a healthcare provider may want to pay special attention to MCV when evaluating a symptom or medical condition. Some of these include:

• Evaluate possible symptoms of anemia such as fatigue, paleness, and dizziness.
• Distinguish between different types of anemia.
• To evaluate other blood abnormalities, such as an abnormal white blood cell or platelet count.
• As an additional test for many diseases.
• Evaluate the prognosis in people with certain medical conditions.

Measurement

The VCM can be measured directly with the analyzer or calculated using a formula. When calculating MCV, the hematocrit (percentage of red blood cells in the blood) is multiplied by ten and divided by the number of red blood cells. This is measured in millions of cells per cubic millimeter of blood.

Sense

MCV is a number that describes the average size of red blood cells circulating in the bloodstream. Therefore, a high MCV will mean that the red blood cells are larger than average. On the contrary, a low MCV will mean that they are below average.

Measuring the average size of red blood cells is very helpful in determining what type of anemia a person has. For instance:

The MCV value is usually quite stable over time. It changes slowly if the person does not receive a blood transfusion.

Restrictions

There are times when the MCV test is not that helpful.

• Post- transfusion : VAW is of little value if the person has received a blood transfusion . In this case, the MCV will show the average size of the transfused red blood cells in combination with the person’s own red blood cells. Therefore, MCV must be measured before blood transfusion.
• Mixed anemia: If a person has more than one type of anemia, MCV will be less helpful. For example, if a person has severe iron deficiency anemia and severe folate deficiency anemia, their VAW may be normal. This is because the first type of anemia causes a low MCV and the second causes a high MCV, resulting in an overall normal reading.
• False positives : MCV can be falsely high in certain settings. This can happen when red blood cells thicken. Sometimes this happens with cold agglutinin disease , paraproteinemia , multiple myeloma , and amyloidosis . It can also occur when a person has very high blood sugar levels.

Similar tests

Mean corpuscular hemoglobin (MCH) is closely related to MCV. Because these indications offer similar information, healthcare providers generally trust MCV and pay less attention to MCH for CBC indications. (MCH should not be confused with MCHC, which is used to diagnose anemia.)

Additional exams

MCV is not used alone; Rather, it is read in conjunction with other tests conducted at the CBC. For example, MCV use can only lead to thalassemia (an inherited disorder that causes destruction of red blood cells) to be misdiagnosed as iron deficiency anemia. This can happen because they both have low MCV levels.

To avoid this, healthcare providers will also look at other things to get a more accurate picture, including:

• Red blood cell count: The red blood cell count (RBC) is the number of red blood cells in a sample of blood.
• Hemoglobin and / or Hematocrit : Hemoglobin is a substance that carries oxygen to the blood. Hematocrit is a measure of the amount of blood that is made up of red blood cells.
• Average corpuscular hemoglobin concentration (MCHC) : MCHC is the average concentration of hemoglobin contained in an erythrocyte.
• Red blood cell distribution width (RDW) : RDW measures how red blood cells differ in size.

Your healthcare provider may order other tests to get more information. These tests can include reticulocyte counts or iron levels .

What to expect

It is quite easy to draw blood. There is little risk associated with a CBC and MCV test. However, there is a small risk of bleeding, bruising, or infection from the blood sample.

Before the test

You do not need to limit your activity level or what you eat before having a complete blood count. The test can be done in the offices and hospitals of most health care providers.

This is generally covered by health insurance when there is a good reason for testing. However, it is best to check with your insurance company to confirm what they will cover.

Be sure to bring your insurance card and, if possible, past CBC results with you to your appointment.

During the exam

MCV is done on a blood sample taken from a vein. If you are in a hospital and you already have a port in Vienna, you can take it from the port.

The lab technician or phlebotomist will clean this area first. They will then put a tourniquet on your arm. Once they find your vein, they will insert a needle into your vein.

You will feel a sharp prick when the needle is inserted into the vein. You may also feel pressure when taking a sample.

After the test is complete, the phlebotomist will remove the needle and apply pressure to the puncture wound until the bleeding stops. Then a bandage or gauze will be applied.

After the test

If it feels good, it will come out immediately after completing the exam.

Side effects are rare, but can include:

• Bleeding People taking blood thinners or bleeding may need to apply pressure to the area to stop the bleeding.
• Hematoma – This is a bruise that can form at the site of the blood sample. It is more common in people who are taking blood thinning medications or who are bleeding.
• Infection – Every time the skin is pierced, there is a small risk of infection.

interpretation of results

Time to results may vary. Sometimes it depends on whether the lab is on site or whether your blood needs to be sent to another lab. In a hospital or clinic with a laboratory, the results may be available the same day.

When reviewing your results, your healthcare provider will find it helpful to compare them to your previous CBCs. This way, they can see if your MCV has changed over time.

Most of the time, a doctor will want to monitor your VAW if you have anemia to determine which type you have. But it is also important, even if you do not have anemia.

Several things can cause a high or low VCM. But your healthcare provider should always interpret MCV in conjunction with other measurements when looking for the cause of anemia.

An unusually high or low VCM can indicate several conditions. In addition to anemia, MCVs outside the expected range can indicate toxicity, vitamin deficiency, and liver disease.

Low MCV (microcytosis)

A low VCM can be observed when:

• Iron deficiency
• Thalassemia
• Chronic disease anemia
• Sideroblastic anemia
• Lead poisoning
• HgC and other hemoglobin hybrids
• Spherocytosis

The lowest MCV level (for example, less than 70, called severe microcytosis) is usually a sign of iron deficiency anemia or thalassemia. However, the conditions do not always fit exactly into these categories. Iron deficiency anemia can sometimes have a normal MCV.

High MCV (macrocytosis)

MCV generally increases with age. In fact, about 30% of older adults will have an elevated VAW for no apparent reason. Conditions associated with a high MCV include:

Higher MCV levels (eg, above 125, known as severe macrocytosis) are generally associated with vitamin B12 or folate deficiency or cold agglutinin disease.

Anemia with normal MCV

Anemias that often have a normal MCV ( normocytic anemias) include:

• Kidney disease (sometimes low MCV levels may also be present)
• Acute blood loss
• Chronic disease anemia
• Endocrine diseases other than thyroid diseases
• Some hemolytic anemias

Assessment of anemia with MCV and other tests

When anemia is present, MCV can help determine the cause. Other tests can be added to the image, including reticulocyte counts, MCHC, and RDW.

The number of reticulocytes

A reticulocyte count (a measure of new red blood cells) is an important first step in determining the cause of anemia. This is because you can classify anemias into two main categories:

• Low production of red blood cells.
• High destruction of red blood cells.

A normal or low reticulocyte count suggests that the body is not taking enough time to make new red blood cells. For example, it can happen when someone is deficient in iron or folic acid.

On the other hand, however, a high count indicates that the body is trying to increase a low red blood cell count. This is seen when red blood cells are lost through bleeding or cell damage.

Combination of MCV and MCHC

The combination of MCV and MCHC can help reduce possible diagnoses. Cells with a low MCHC are called hypochromic , which means light in color.

The following table shows which conditions are associated with different combinations of MCV and MCHC measurements.

Combination of MCV and RDW

RDW describes the change in the size of red blood cells. Anisocytosis is the medical term for red blood cells of various sizes.

For example, in sideroblastic anemia, most cells may be large, but some cells will be small. In this situation, the MCV may be normal, but the RDW will be high.

Other tests

Other tests may be helpful in conjunction with MCV and other red blood cell counts. They include:

Blood differential : The differential blood count can provide additional information about anemia. This test shows differences in the size, shape, or color of cells. Other results may include:

• Target Cells and Acanthocytes (Abnormal Red Blood Cells) Seen in Thalassemia
• Hypersegmented neutrophils (a type of white blood cell) seen in folate deficiency anemia.
• Spherocytes in spherocytosis
• Sickle Cells in Sickle Cell Anemia
• Howell-Jolly bodies in people without a spleen
• Nuclear red blood cells seen in babies or adults who are critically ill

Iron tests : Serum iron, iron-binding capacity, and serum ferritin may be beneficial, especially with a low MCV. For example, MCV will be low in sideroblastic anemia, but iron stores can be very high.

Vitamin B12 levels : Levels of vitamin B12 can be used to diagnose deficiency in macrocytic anemia.

Hemoglobin Electrophoresis (HE) : HE detects signs of beta thalassemia (an inherited blood disorder). However, you cannot test for alpha thalassemia (inherited anemia).

Bone marrow biopsy: A bone marrow biopsy can help determine the number and types of cells in the biopsy. It can also be used to evaluate iron.

Use of MCV without anemia

The MCV test can provide important information even if the red blood cell count is normal. Here are some examples:

• Predicting mortality from esophageal cancer
• Assessment of prognosis in chronic kidney disease (CKD)
• Predict how a person with rectal cancer might respond to chemotherapy and radiation.
• Evaluation of cognitive functions (thinking and memory) in the elderly

For example, a 2017 study found that people with high MCV kidney disease are more than twice as likely to die from all causes of death. In addition, they were 3.5 times more likely to have heart disease than those with normal MCV.

Follow up

Subsequent tests depend on the results of the MCV test and other measurements.

Summary

The MCV is useful in evaluating anemia and several other medical conditions. But they generally don’t look at it alone. Instead, your healthcare provider will review the MCV along with other data on the CBC to get a complete picture.

In addition to anemia, MCVs outside the expected range can indicate toxicity, vitamin deficiency, and liver disease.

MCV can also help determine the prognosis for certain cancers and chronic kidney diseases. In addition, it can be used as a tool to assess cognitive performance in older adults.

Get the word of drug information

The MCV test, especially when combined with other CBC numbers, can help diagnose anemia, plan treatment, or predict the prognosis for other conditions.

Unfortunately, these small numbers in CBC can easily be overlooked. Therefore, it is a good idea to defend yourself and ask your doctor about any levels that are marked as abnormal.