MCV value: what does it say about your blood?

Your MCV value tells you, in a single number, how large your red blood cells are on average. MCV stands for mean corpuscular volume and is measured in femtolitres (fL). It's a standard part of a complete blood count and helps your doctor trace the cause of anaemia or fatigue.

Honestly, of all the abbreviations on a lab report, MCV is one of my favourites. It doesn't tell you how many red cells you have, but whether they're the right size.

What does MCV actually measure?

MCV measures the average volume of a single red blood cell in femtolitres (fL). Think of it as the average shoe size of your red cells. Together with your haemoglobin and red cell count, MCV shows whether your cells are normal, too small or too large.

This value is one of the erythrocyte indices, first described by Wintrobe in 1929 (Sarma, 1990). A cell's size turns out to be as telling as the cell count.

What is a normal MCV value?

In adults the normal MCV range usually sits between 80 and 100 fL. Within that range your red cells are a normal size (normocytic). The exact limits vary slightly per laboratory, since equipment and reference groups differ.

• 80 to 100 fL: normal (normocytic)
• Below 80 fL: microcytic, meaning red cells that are too small
• Above 100 fL: macrocytic, meaning red cells that are too large

An abnormal number is not a diagnosis. It's a clue that tells your doctor where to look next.

What does a low MCV (microcytic) mean?

A low MCV means your red cells are smaller than usual. That often points to a problem making haemoglobin, the protein that carries oxygen. Iron deficiency is by far the most common cause (Camaschella, 2015).

Causes a doctor may consider:

• Iron deficiency: without enough iron, your body makes smaller cells with less haemoglobin.
• Chronic inflammation or disease: iron is present but temporarily hard to use.
• Thalassaemia: an inherited condition that changes how haemoglobin is made.
• Lead exposure: a rarer cause that can disrupt cell formation.

With a low MCV, ferritin (your iron stores) is often measured too. To see how that works, read how to detect iron deficiency with a blood test. Don't start iron supplements on your own, because with thalassaemia extra iron does not help and may build up unwantedly.

What does a high MCV (macrocytic) mean?

A high MCV means your red cells are larger than usual, which doctors call macrocytosis. The cause often lies in a shortage of vitamin B12 or folate, both needed for cell division (Stabler, 2013). Without that signal, a cell keeps growing into an oversized one.

Common causes include:

• Vitamin B12 deficiency: a frequent reason for a raised MCV.
• Folate deficiency: folate is also needed for healthy cell division.
• Alcohol: heavy long-term drinking can affect red cell production.
• Underactive thyroid: hypothyroidism sometimes goes with a mildly raised MCV.
• Certain medicines: drugs such as methotrexate act on cell division.

A B12 or folate shortage can come with tingling in the hands or feet, trouble concentrating or pale skin. Megaloblastic anaemia from B12 deficiency shows up clearly in the blood count (Green, 2017). Read more in our guide on vitamin B12 deficiency.

What is the difference between MCV, MCH and MCHC?

MCV, MCH and MCHC describe your red cells together, each from a different angle. MCV is about size, MCH about the amount of haemoglobin per cell, and MCHC about how concentrated that haemoglobin is. Doctors always read them side by side (Sarma, 1990).

A small, pale cell (low MCV and low MCHC) is a classic pattern in iron deficiency. That's how the three values add up to a clearer picture.

MCV in context: reading it with other values

MCV is rarely judged on its own. Combined with other values, it points your doctor towards a cause. A few common patterns:

• Low MCV and low ferritin: fits iron deficiency anaemia.
• High MCV and low B12: fits megaloblastic anaemia.
• Normal MCV and low haemoglobin: fits normocytic anaemia, for example in chronic disease or kidney problems.

What questions can you ask your doctor about your MCV?

An abnormal MCV raises questions, and walking in prepared helps. These are worth taking to your GP:

• Does this MCV value fit the symptoms I have, such as fatigue?
• Could my diet or medication play a role in this result?
• Which follow-up tests make sense, for example iron, ferritin, vitamin B12 or folate?
• What would be a logical next step if something turns up?
• When would it make sense to test my blood again?

If you want a broader view of your red cells, an anaemia panel can measure MCV alongside iron, ferritin and vitamins.

Frequently asked questions

Can my MCV be normal while I still have anaemia?

Yes, this happens in normocytic anaemia. Your red cells are a normal size, but there are too few of them or they hold too little haemoglobin. Chronic disease and kidney problems can play a part.

How long until MCV normalises after treatment?

Red blood cells live about 120 days. So it can take 2 to 4 months for MCV to settle again after a deficiency is addressed.

Is MCV measured as standard?

Yes. MCV is a standard part of the blood count (CBC) and is included automatically in almost every full blood test.

Sources

1. Sarma PR. Red Cell Indices. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 152.
2. Camaschella C. Iron-deficiency anemia. N Engl J Med. 2015;372(19):1832-1843. PMID: 25946282.
3. Stabler SP. Vitamin B12 deficiency. N Engl J Med. 2013;368(2):149-160. PMID: 23301732.
4. Green R. Vitamin B12 deficiency from the perspective of a practicing hematologist. Blood. 2017;129(19):2603-2611. PMID: 28360040.

Every blood test result at Vital Check includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.