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Blood test

MCV test

MCV test: what it measures, why a doctor orders it, how to prepare, and what a high or low result can mean - with private and NHS access routes in the UK.

Key facts

At a glance

  • What it measures: the mean cell volume - the average size of your red blood cells.

  • Why it is ordered: to work out the likely cause of an anaemia, since different deficiencies change red cell size in opposite directions.

  • No fasting or special preparation is needed for this test on its own.

  • Reference ranges: the adult interval describes average red cell size in femtolitres and is printed with every full blood count. Every laboratory publishes its own interval, so the range printed on your report is the one that applies to you.

  • A raised result with large cells points towards B12 or folate deficiency, alcohol, thyroid disease or some medications. A low result with small cells points towards iron deficiency or an inherited condition such as thalassaemia trait.

  • Results are usually back within 24-48 hours when taken privately, and often the same day for urgent requests.

The full picture

What this test tells you, and how to get it

The MCV test measures the mean cell volume - the average size of your red blood cells. Doctors most often request it to work out the likely cause of an anaemia, since different deficiencies change red cell size in opposite directions. No fasting or special preparation is needed for this test on its own. The adult interval describes average red cell size in femtolitres and is printed with every full blood count, and reference intervals genuinely differ between laboratories, so no single number should be treated as a universal cut-off - your result is always read against the range printed on your own report. Broadly, a raised result with large cells points towards B12 or folate deficiency, alcohol, thyroid disease or some medications, while a low result with small cells points towards iron deficiency or an inherited condition such as thalassaemia trait, and either finding is interpreted alongside your symptoms, medication and other results rather than in isolation. Results are usually back within 24-48 hours when taken privately, and often the same day for urgent requests.

In the UK there are two routes to this test. Your NHS GP can arrange it free of charge when it is clinically indicated, though getting the appointment, the blood draw and the follow-up discussion can add days to weeks depending on local demand. Privately, the MCV test can usually be booked within days - through a private GP, a walk-in phlebotomy clinic or a self-request home-testing service - and it is one of the most useful clues on a full blood count. A private result still deserves a clinician's interpretation: an isolated number without context is where most confusion about blood tests begins.

A quiet reminder

This guide is for information, not medical advice.

Your own clinician knows your history and can tell you which parts apply to you. Reference ranges vary between laboratories - always read your result against the interval printed on your own report. Next review of this page: 2027-09-27.

Frequently asked

Common questions about MCV test.

Quick, plain-English answers to what people ask us most.

  • What does the MCV test measure?

    MCV stands for mean corpuscular volume, and it measures the average size of your red blood cells. It's a standard part of a full blood count and helps classify the type and possible cause of anaemia if present.

  • Why would a doctor order an MCV test?

    It's typically checked alongside haemoglobin when investigating fatigue, pallor, or shortness of breath, or simply as part of a routine full blood count. It helps narrow down whether anaemia, if present, relates to iron deficiency, vitamin B12 or folate deficiency, or other causes.

  • Do I need to prepare for the test?

    No fasting or special preparation is needed for this test, as it's part of a standard full blood count.

  • What happens during the test?

    A routine blood sample is taken from a vein in your arm, taking just a few minutes, with the result generated as part of your full blood count analysis.

  • Does it hurt or carry risks?

    You'll feel a brief pinch from the needle, similar to any blood test, with negligible risk.

  • How long do results take?

    Results are typically available within 24 to 48 hours.

  • What do abnormal results mean, and what happens next?

    Small red cells (low MCV) often point towards iron deficiency or, less commonly, thalassaemia trait, and usually prompt an iron studies check. Large red cells (high MCV) can relate to vitamin B12 or folate deficiency, alcohol intake, or thyroid issues, and typically lead to further targeted blood tests. Your doctor will use the MCV alongside other results to guide the next step rather than relying on it alone.

  • Is this test available on the NHS, and how much does private testing cost?

    MCV is included in NHS full blood count testing, though routine GP access and follow-up investigations can take time. Private testing typically offers results within days with doctor review. Cost varies by provider.

  • Is the MCV test accurate and reliable?

    Automated laboratory analysis of MCV is highly accurate and a well-established, routine part of blood testing worldwide.

  • How do I book this test privately, and how quickly can I be seen?

    You can book a private full blood count online, often within a day or two, with a doctor available to explain your MCV result and recommend any follow-up tests if needed.