MCV value: what does it say about your blood?

Your lab report is full of abbreviations, but MCV is one I always pause on. In a single number it tells you how big your red blood cells are on average. Not how many you have, but whether they are the right size. And that size often points your doctor straight towards the cause of anaemia or fatigue.

My stance up front: an abnormal MCV is not a diagnosis, but a signpost. The nice thing is that the direction in which the cells deviate (too small or too large) often already reveals where the follow-up test should start. That saves guesswork.

What exactly does MCV measure?

MCV stands for mean corpuscular volume, the average volume of a red blood cell, expressed in femtolitres (fL). Think of it as the average shoe size of your red blood cells. Together with your haemoglobin and the number of erythrocytes, MCV shows whether your cells are normal, too small or too large. It is part of a standard complete blood count.

What is the normal value for MCV?

In adults the normal value for MCV lies between 80 and 100 fL, and it is the same for men and women. Within that range your red blood cells are normal in size (normocytic). The exact limits vary slightly per laboratory, so compare your result with the reference value on your own lab form. And normal is not the same as unchanged: if your value moves from 88 to 97 fL over a year, that is a change worth discussing, even though both numbers stay inside the normal range. If you want the normal range in more detail, you will find it under the MCV blood value.

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

MCV as a signpost: which direction points to what?

The real power of MCV lies in combining it with other values. The table below is your decision aid: per pattern you see what it classically fits and which follow-up test is logical. It remains a line of reasoning, not a diagnosis.

The blind spot in this decision tree

The chart above works as long as only one thing is going wrong at a time. Too small sends you towards iron, too large towards vitamin B12 or folate, and normal means there is no need to look further. That last branch is the weak one.

Suppose you are short of iron and short of B12 at the same time. Your body then makes two kinds of cell at once: some too small because of the iron, some too large because of the B12. The lab does not give you two numbers, but one average across all the cells together. Small and large cells pull that average towards each other, and an unremarkable 91 fL is what comes out. The chart then puts you on the branch where there is nothing to find, while in reality you are short on two fronts.

So the chart is missing a question. After "is the MCV normal?" one more should follow: "and are the cells all close to each other in size?" That second answer is called RDW, and it is usually already on the same form. The RDW expresses how far the cell sizes diverge from one another. One kind of cell in one size produces a low RDW, a mixture of small and large cells a high one. That is how the RDW can climb while the MCV still sits in the middle of the band, and why a normal MCV only reassures once the RDW is not standing out above it.

If you have landed on that normal branch yourself, do not stop at the one number. An MCV of 91 fL clears you of nothing while your symptoms persist. Look on your result for the RDW first, and then for folate, vitamin B12 and ferritin, in so far as they were measured. If they are not there, put it to your GP that an average inside the band can mask two opposing deficiencies.

What does a low MCV (microcytic) mean?

A low MCV means your red blood cells are smaller than normal. That often points to a problem making haemoglobin. Iron deficiency is by far the most common cause. Other possibilities a doctor may consider are chronic inflammation, thalassaemia (a hereditary condition) and, more rarely, lead exposure.

With a low MCV, ferritin is often also measured, your iron store. To learn how that works, read how to detect iron deficiency with a blood test. Important: do not start iron pills on your own. With thalassaemia extra iron does not help and may even accumulate undesirably.

What does a high MCV (macrocytic) mean?

A high MCV means your red blood cells are larger than normal, which doctors call macrocytosis. The cause is often a deficiency of vitamin B12 or folate, two substances needed for cell division. According to the NHG anaemia guideline, among others, a B12 deficiency is a common reason for a raised MCV in the Netherlands. Other causes are prolonged heavy alcohol use, a slow thyroid and certain medicines.

A B12 or folate deficiency can go together with tingling in hands or feet, concentration problems or pale skin. Read more in our guide to vitamin B12 deficiency.

A mildly raised MCV and nothing else: look at the tube first

Before you read a mildly raised MCV as a finding, there is a duller explanation you want to rule out first. Blood for a blood count goes into a tube containing EDTA, a substance that prevents clotting. Red blood cells slowly take up a little fluid in such a tube and swell as a result. The longer the blood stands before the analyser measures it, the larger the cells are at the moment of measurement.

In a sample analysed only after about 24 hours, for instance because it was first transported to another laboratory, the MCV can therefore come out artificially higher than it was at the draw. The MCHC usually moves the other way, because the same amount of haemoglobin is spread across a larger cell volume. That combination is the giveaway.

What that means for you: an isolated, mildly raised MCV while your haemoglobin, your red blood cell count and the rest of your blood count are normal is first a question about the sample and only then a question about you. Feel free to ask how much time passed between the draw and the measurement. If the value stays the same on a fresh, promptly processed tube, it is worth looking into further with your GP.

What is the difference between MCV, MCH and MCHC?

MCV, MCH and MCHC together describe your red blood cells, but 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 in combination. A small, pale cell (low MCV and low MCHC) classically fits with iron deficiency.

Why you should not start supplements on your own

It is tempting to head straight to the supplement shop with an abnormal MCV, but that is often unwise. The direction of the deviation determines which cause is likely, and those causes call for different approaches. If you take iron while your high MCV is due to a B12 deficiency, you solve nothing and delay the right treatment. If you take iron while your low MCV belongs to thalassaemia, iron may even accumulate undesirably. So only start supplementing after the cause has been confirmed with a blood test and you have discussed it with a doctor. A targeted test of your iron status or vitamins gives the direction; you agree the right dose and duration with your GP. That way you avoid treating a symptom without knowing its source.

What questions can you ask your doctor about your MCV?

• Does this MCV value fit my symptoms, such as fatigue?
• Could my diet or medication play a role?
• Which follow-up tests are worthwhile: iron, ferritin, B12 or folate?
• When is it useful to have blood drawn again?

To map your red blood cells more broadly, 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, that can happen with normocytic anaemia. Your red blood cells are then normal in size, but there are too few of them or they contain too little haemoglobin. Chronic disease and kidney problems can play a role.

How long until MCV normalises after treatment?

Red blood cells live about 120 days on average. So it can take 2 to 4 months for the MCV to reset after a deficiency is addressed.

Is MCV measured as standard?

Yes. MCV is part of the standard blood count and is included automatically in almost any full blood test.

Sources

• NHG (Dutch College of General Practitioners). NHG anaemia guideline. Accessed 2026.
• RIVM (National Institute for Public Health). Vitamin and mineral status of the Dutch population. Accessed 2026.

Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. Always discuss treatment decisions with your own GP.