A high MCV means your red blood cells are larger than normal. While a high MCV can be associated with a group of cancers called myelodysplastic syndromes, other causes of high MCV, such as vitamin deficiency or liver disease, are far more common.

A measurement of mean corpuscular volume (MCV) is included in a complete blood count (CBC). A CBC is a common blood test that measures the numbers, types, and sizes of different blood cells.

Having a high MCV means your red blood cells are larger than typical red blood cells. While a high MCV has many common causes, it can also be a sign of myelodysplastic syndromes, a group of cancers that affect blood.

In this article, we take a closer look at MCV, its association with cancer, and the health conditions that more commonly cause high MCV.

An MCV test measures the average size of your red blood cells (RBCs). RBCs are the cells that transport oxygen to the organs and tissues of your body.

It’s most likely that you’ll have an MCV test as a part of a CBC that’s done during a routine physical. It may also be used to help diagnose or monitor certain blood disorders.

The ranges for MCV are:

  • Normal: The normal range for MCV is 80 to 100 femtoliter (fL). This means your RBCs are a typical size. RBCs that fall into this range are called normocytic.
  • Low: A low value for MCV is anything under 80 fL. This means your RBCs are smaller than normal. The term for this is microcytic.
  • High: A high MCV value is anything over 100 fL. Having a high MCV means your RBCs are larger than normal. The term for this is macrocytic.

Does a high MCV cause symptoms?

High MCV doesn’t always cause symptoms. However, sometimes high MCV is associated with certain types of anemia. This means it’s possible that you can experience some of the following symptoms if you have anemia with high MCV:

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Myelodysplastic syndromes (MDS) are a group of cancers sometimes associated with high MCV. The American Cancer Society estimates that about 10,000 people in the United States receive a diagnosis of MDS each year, although this number may be higher.

MDS happens when immature blood cells in the bone marrow become abnormal and have trouble developing into mature cells. These abnormal cells die early, meaning your body doesn’t have enough healthy blood cells. This possibly results in lower than normal blood counts on blood work.

Since MDS affects the blood cells of the bone marrow, the RBCs, white blood cells, and platelets can all be affected. RBCs are one cell type that can be involved in MDS. Cells impacted by MDS can have dysplasia, which means they have an abnormal size, shape, or number.

When MDS affects RBCs, it can lead to anemia. In fact, anemia is the most common finding in MDS.

Does a high MCV affect cancer outlook?

A higher MCV may point to a poorer outlook for some cancers. Why exactly this is the case is not known. It may be linked with the association of high MCV with anemia and nutritional deficiencies.

Some examples of cancers in which higher MCV has been associated with poor outlook include:

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Several other conditions can cause a high MCV. Some of the most common include vitamin B12, folate, and copper deficiencies.

Vitamin B12 deficiency can happen due to:

There are also several potential causes of folate deficiency, including:

Other causes of high MCV that may be unrelated to a vitamin B12 or folate deficiency include:

Sometimes high MCV does not need to be treated. This is typically the case if all of the following are true:

  • MCV is less than 115 fL
  • you don’t have anemia
  • there are no other health concerns related to your MCV or other test results

High MCV that’s concerning or is causing symptoms is typically treated by addressing the condition that’s causing it. For example, supplementation can treat vitamin B12 or folate deficiencies.

If you have cancer and a high MCV, your care team will develop a treatment plan for that cancer. It’s possible your MCV values will return to the normal range with treatment.

MCV measures the size of your RBCs. A high MCV means your RBCs are larger than normal, a condition called macrocytosis. Some people with high MCV have anemia.

A high MCV can be associated with MDS, an uncommon type of cancer. It affects cells in the bone marrow, including RBCs.

However, it’s more likely that high MCV values are due to other causes, such as liver disease, heavy alcohol use, certain medications, or deficiencies in vitamins like B12, copper, and folate.

It’s important to talk with a doctor if you have symptoms of anemia. These include fatigue, dizziness, and shortness of breath. Your doctor can do tests, including a CBC, to help figure out what may be causing your symptoms.