Mean Corpuscular Volume (​MCV) Blood Test

Written by Sonya Collins
Medically Reviewed by Laura J. Martin, MD on June 29, 2025
6 min read

MCV stands for mean corpuscular volume. An MCV blood test measures the average size of red blood cells, which have the critical job of carrying oxygen to your organs. If they’re too big or too small, it could be a sign of trouble, like anemia or a vitamin deficiency. 

What does an MCV blood test measure? 

The test measures the volume or size of your red blood cells in femtoliters (fL), which are one quadrillionth of a liter. 

“An MCV blood test alone is not a test that a doctor orders,” says Roy Silverstein, MD, professor of medicine at the Medical College of Wisconsin in Milwaukee. “Rather, it’s part of a complete blood count, or CBC.” That’s a routine panel of blood tests that doctors order often. You might have a CBC as part of a routine annual physical, before having surgery, or when your doctor is investigating a specific health concern you’re having. 

A CBC includes tests to measure the size or number of the following:

  • Red blood cells, which carry oxygen
  • White blood cells, which fight infection
  • Hemoglobin, the protein in red blood cells that transports oxygen
  • Hematocrit, the amount (percentage by volume) of red blood cells in your blood
  • Platelets, which help blood clot

Your doctor might order this test to:

  • Check your overall health as part of routine preventive care 
  • Diagnose or rule out a medical condition
  • Monitor a health condition you already have
  • See how well a medication is working 

If you have certain symptoms, your doctor might order a CBC, which includes an MCV blood test. These symptoms include:

  • Shortness of breath
  • Weakness or fatigue
  • Headache
  • Dizziness
  • Irregular heartbeat

You don’t need to do anything to prepare for an MCV blood test. But because this test is often done along with other tests, your doctor might ask you not to eat or drink anything for a certain period of time before the blood is taken in preparation for the other tests. 

An MCV blood test is simple and fast. It will be over in less than five minutes.

You’ll sit in a chair – often a special chair with an armrest designed for taking blood. A health care provider will tie a rubber cord around your arm above the place where they will insert the needle. This restricts the blood flow to the right area and makes it easier to see the vein and get blood from it. They will insert a small needle into a vein in your arm to take a blood sample. 

You might feel a little sting or prick when the health care professional inserts or removes the needle. After they insert the needle, they will draw the blood directly into a vial or test tube. Depending how many other blood tests your doctor ordered, the health care provider may draw more than just the amount of blood needed for the MCV test. 

The results of an MCV blood test alone cannot diagnose any health condition, “but it can tell you a lot,” Silverstein says. Your doctor might use these results along with other information about your health, such as physical symptoms you’re having and other test results, to confirm or dismiss their suspicion about a specific health problem. 

“The results may be helpful in pointing the doctor more efficiently towards the final diagnosis,” Silverstein says. 

MCV blood test results report the average size of your red blood cells in femtoliters (fL). The doctor will want to know whether that size is within the normal, low, or high range. 

Normal MCV

A normal MCV is between 80 and 100 fL. Any rest result in that range is considered normal, but it’s sometimes possible to have anemia and still have a normal MCV. 

Low MCV

An MCV of less than 80 fL, a condition called microcytosis, is considered low and could be a sign of:

  • Some types of anemia, including iron deficiency anemia, the most common type, which happens when you don’t have enough iron in your body. Low iron can have a number of causes that your doctor might want to investigate. 
  • Thalassemia, a group of blood disorders that are passed down from parents to their children, which causes low levels of red blood cells and hemoglobin and causes anemia.
  • Lead poisoning.

“If the patient has no family history of thalassemia, hasn’t had any exposure to lead, and all other blood counts are normal, it’s likely going to turn out to be iron deficiency,” Silverstein says. 

Some non-iron-deficiency anemias can also cause low MCV. They include:

  • Sideroblastic anemia, where you have enough iron in your body but your blood cells aren’t taking it up correctly, which leads to an iron overload.
  • Anemia of chronic disease, which is also due to the body not using iron properly and seen in people who have inflammatory diseases, such as diabetes. 

“Anemia of chronic disease is something that a doctor’s going to look at if you have low MCV but don’t have iron deficiency,” Silverstein says. “Then the most likely scenario for most adult patients is going to be anemia of chronic disease, which you might see in patients who have lupus, rheumatoid arthritis, chronic heart failure – many diseases of modern life are associated with inflammation.” 

High MCV

An MCV of more than 100 fL, a condition called macrocytosis, is considered high and could be a sign of:

  • Vitamin B12 deficiency, caused by an autoimmune disorder called pernicious anemia or another cause
  • Folate (vitamin B9) deficiency
  • Liver disease
  • Bone marrow dysfunction caused, for example, by certain types of leukemia
  • A side effect of certain chemotherapy drugs

MCV stands for “mean corpuscular volume,” which refers to the average size of your red blood cells. An MCV blood test is part of routine blood work called a complete blood count or CBC. MCV test results alone cannot diagnose disease, but if your doctor ordered a CBC, which includes MCV, the results might help point the doctor toward a diagnosis.

What does MCV mean in a blood test when it is high?

A high MCV alone is not enough to diagnose any health condition, but it might help your doctor  narrow down which possible diagnoses they should consider. 

Is it better to have high or low MCV?

It’s neither better to have a high MCV nor a low MCV. Ideally, you want to have a normal MCV that falls between 80 and 100 fL. But even if your MCV falls outside of this range, that doesn’t mean you definitely have a serious health condition. 

What is an alarming MCV level?

There’s not a universally “alarming” MCV level that all doctors agree on, but an abnormal level might be alarming if it also came with other abnormal blood tests and physical symptoms of a serious health condition, such as leukemia.

What does it mean when your MCV is low?

A low MCV alone may not mean anything serious at all, but combined with other relevant symptoms and test results, it could point to the possibility of iron-deficiency anemia or an inherited blood disorder called thalassemia. 

Can dehydration cause high MCV?

Dehydration can make the blood more concentrated and cause the red blood cells to look larger than they are because they are squeezed into less space. Dehydration doesn’t raise MCV, but it can cause a falsely high MCV result.