Mean Corpuscular Volume (MCV)
MCV is the average size of your red blood cells. It is a handy clue if you are anaemic: red cells that are larger than usual often point to a vitamin B12 or folate shortage, while smaller-than-usual cells most often mean low iron. On its own a slightly off result is common and rarely a worry — your GP reads it together with the rest of your blood count.
Standard CareWhat is mean corpuscular volume (mcv)?
MCV (mean corpuscular volume) is a calculated value on your full blood count (FBC) that tells you the average volume — in other words, the average size — of your red blood cells, measured in femtolitres (fL), a very tiny unit, because red blood cells are microscopic. Red blood cells are the cells that carry oxygen around your body, and their size is closely related to how well they were made. When red cells are larger than usual, doctors describe them as macrocytic (macro = large). When they are smaller than usual, the term is microcytic (micro = small). A normal-size result is called normocytic. MCV is part of a group called the red cell indices, which also includes MCH (mean corpuscular haemoglobin — the average amount of oxygen-carrying protein per cell) and MCHC (mean corpuscular haemoglobin concentration). Together these indices help your GP work out not just whether your red cells are abnormal, but what kind of problem is most likely.
Why is it tested?
MCV is reported automatically on every full blood count. It is most useful when haemoglobin or the red blood cell count is low, because the size of the cells gives your GP a strong clue about the cause. Large cells (high MCV) most often indicate a deficiency of vitamin B12 or folate, both of which are needed for the DNA replication that builds red blood cells — without enough of either, the cells grow large but fail to divide properly. Large cells can also reflect liver disease or an underactive thyroid (hypothyroidism). Small cells (low MCV) most often point to iron deficiency anaemia, in which the cells are small and pale because there is not enough iron to fill them with haemoglobin. Small cells can also occur in an inherited condition called thalassaemia. MCV is also checked when your GP is investigating symptoms of anaemia — tiredness, breathlessness, pale skin, or dizziness — or when monitoring a known condition such as iron deficiency, inflammatory bowel disease, or liver disease.
Reference range (Australia)
Full blood count reference intervals are set by each laboratory and depend on the analyser platform used. The MCV reference range is generally the same for men and women, but the interval printed on your own pathology report is the authoritative value for your result.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A low MCV means your red blood cells are smaller than the reference range on your report. The most common cause is iron deficiency anaemia, in which the cells are small and pale (hypochromic) because there is not enough iron to fill them with haemoglobin. An inherited condition called thalassaemia can also produce small red cells, even when iron stores are normal. Your GP will typically check ferritin and iron studies when MCV is low to confirm whether iron deficiency is the cause. If iron is normal, thalassaemia or another cause may need investigation.
Your MCV falls within the range printed on your report, suggesting your red blood cells are normal in size. If your haemoglobin is also normal and you feel well, no follow-up is usually needed. If you have ongoing symptoms such as tiredness or breathlessness, let your GP know — they may wish to check related markers such as ferritin or vitamin B12.
A high MCV means your red blood cells are larger than the reference range on your report. The most common reasons are deficiency of vitamin B12 or folate — both needed for normal red cell production — or liver disease or hypothyroidism (an underactive thyroid). This pattern is called macrocytic anaemia when it is accompanied by a low haemoglobin. A raised MCV on its own is not a diagnosis: it is a pointer. Your GP will usually check vitamin B12 and folate levels, thyroid function, and liver function to work out the underlying cause. If you have a mildly raised MCV and feel well, it is still worth discussing with your GP at your next visit so they can decide whether further tests are needed.
What can affect your result
MCV reflects how well red blood cells are being made and whether the raw materials for production are adequate. Vitamin B12 and folate are both needed for the DNA replication that drives red blood cell division. When either is deficient, the bone marrow produces large, immature cells that cannot divide properly — this raises the MCV. Iron deficiency has the opposite effect: without enough iron to build haemoglobin, the bone marrow produces small, pale cells, lowering the MCV. Liver disease can raise MCV because the liver is involved in red cell membrane composition; alcohol use is a common clinical cause of a mildly raised MCV through this and other mechanisms. Hypothyroidism (an underactive thyroid) is another recognised cause of a raised MCV, as thyroid hormones influence red cell production. Thalassaemia — an inherited condition affecting haemoglobin production — characteristically produces small red cells and a low MCV, and may be confused with iron deficiency. Iron studies help distinguish the two. Certain medications, including methotrexate and some antiretrovirals, can interfere with folate metabolism and raise MCV.
When to act
If your MCV is outside the reference range on your report, discuss it with your GP. They will read it alongside your haemoglobin, red blood cell count, and MCH on the same report, and consider your symptoms and history, to work out the most likely cause and whether any follow-up tests are needed. A mildly raised or lowered MCV in an otherwise well person is often incidental and may not require urgent action, but it is worth tracking over time — trends in MCV are more informative than a single result. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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