Mean Corpuscular Volume (MCV) – Understanding Your Blood Test Result

Section Editor: Christopher McCudden Ph.D., DABCC, FADLM, FCACB
September 15, 2026

MCV stands for mean corpuscular volume. It measures the average size of your red blood cells, the cells that carry oxygen throughout your body. Doctors don’t order MCV on its own. It is one of the results that appears automatically with a complete blood count, often shortened to CBC.

This article explains what MCV measures and what a high or low result can mean. It also explains why doctors find red blood cell size so useful when working out the cause of anemia.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What does the MCV test measure?

Your bone marrow, the soft tissue inside your bones, makes red blood cells. When the marrow has everything it needs, it produces cells of a fairly uniform size. When something is missing or interfering, the cells it makes come out too small or too large.

The laboratory analyzer measures many thousands of your red blood cells and reports the average size. That average is your MCV. Because different causes of anemia change cell size in different directions, MCV is often the first clue to why your blood count is low.

Your report may show MCV in femtolitres, written fL, printed next to a reference range. A typical adult range is about 80 to 100 fL, and exact ranges vary by laboratory

Why does red blood cell size matter?

Anemia means there are not enough healthy red blood cells to carry oxygen well. Anemia is not a diagnosis on its own. It is a finding that needs an explanation, and MCV is one of the fastest ways to narrow that explanation down.

Doctors group anemia into three types by cell size. Small cells are called microcytic, normal-sized cells normocytic, and large cells macrocytic. Each group points toward a different set of causes, so knowing the MCV turns a long list of possibilities into a short one. That is why MCV is reported even when nobody asks about it specifically.

How is the MCV test performed?

MCV is measured on a small sample of blood, usually taken from a vein in your arm. No fasting is needed. It is calculated automatically as part of a complete blood count, so you do not need to request it separately.

If your MCV is abnormal, your doctor may ask the laboratory to examine a blood smear. This is a drop of your blood spread on a glass slide and looked at under a microscope. It shows the shape and appearance of individual cells rather than an average.

What do MCV results mean?

MCV is read alongside your hemoglobin, your hematocrit, and the other red cell measurements.

A normal MCV — a result inside the reference range means your red blood cells are of average size. If your hemoglobin is also normal, this is reassuring. If your hemoglobin is low with a normal MCV, that pattern has its own set of causes.
A low MCV — a result below the reference range means your red blood cells are smaller than average. This is called microcytosis. The most common cause is low iron. Inherited conditions that affect hemoglobin can also produce small cells.
A high MCV — a result above the reference range means your red blood cells are larger than average. This is called macrocytosis. Common causes include low vitamin B12 or folate, regular alcohol use, an underactive thyroid, and some medicines.

An MCV slightly outside the range with a normal hemoglobin is a common and often unimportant finding. The combination of MCV and hemoglobin gives it meaning.

What conditions and factors can affect MCV?

Common reasons MCV can be low

Iron deficiency — the most frequent cause. Without enough iron, the marrow makes smaller cells containing less hemoglobin.
Thalassemia trait — an inherited difference in how hemoglobin is made. It produces small cells lifelong, often with a normal or near-normal hemoglobin, and is usually harmless in the trait form.
Long-standing inflammation — chronic conditions can modestly lower MCV, though they more often leave it normal.
Lead exposure — an uncommon cause, usually considered only when there is a reason to suspect it.

Common reasons MCV can be high

Low vitamin B12 or folate — both are needed for cells to divide properly. Without them, the marrow releases large, immature cells.
Regular alcohol use — one of the commonest causes of a mildly raised MCV, and it can occur before any other test changes.
An underactive thyroid — which slows cell production and increases cell size.
Liver disease — which changes the membrane surrounding red blood cells.
Some medicines — including certain drugs used for seizures, autoimmune conditions, and cancer. Do not stop any medicine because of a blood test. Ask the doctor who prescribed it.
The marrow is working hard — after bleeding or during recovery from anemia, young red blood cells are released early, and these are larger than mature ones.

MCV can be normal even when the cells are not. If you have both iron deficiency, which makes cells small, and B12 deficiency, which makes them large, the average can land in the normal range while neither problem is normal. This is one reason the RDW result, which measures how much cell size varies, is read alongside MCV.

What other tests are ordered with MCV?

Hemoglobin and hematocrit — which show whether anemia is present at all.
RDW — which shows how much your cell sizes vary, and often changes before MCV does.
MCH and MCHC — which describe how much hemoglobin the cells contain.
Ferritin and iron studies — when a low MCV suggests iron deficiency.
Vitamin B12 and folate — when a high MCV suggests a vitamin cause.
Thyroid function tests and liver tests — when a high MCV has no obvious explanation.
A blood smear — to look at the cells directly.

What happens after an MCV test?

A mildly abnormal MCV with a normal hemoglobin is often repeated, particularly if you feel well. Many people run slightly outside the printed range without any problem, and your own previous results are the most useful comparison.

If your hemoglobin is low as well, your doctor uses the MCV to decide which tests to order next. A low MCV usually prompts iron studies. A high MCV usually prompts vitamin B12 and folate testing, along with questions about alcohol and a review of your medicines. Treatment addresses the cause rather than the MCV itself, and the cell size returns toward normal as the underlying problem is corrected. This takes weeks to months, because red blood cells live for around four months and the population has to turn over.

Questions to ask your doctor

What was my MCV, and what is the reference range at this laboratory?
Is my hemoglobin normal, and am I anemic?
How does this compare with my previous results?
Do you think this points toward iron, vitamin B12, or something else?
Could any of my medicines be affecting this result?
Do I need iron studies, or vitamin B12 and folate testing?
Do you want to repeat the test, and if so, when?
Could this be an inherited difference that has always been there?