Quick answer, as of October 2026: MCV is the average size of your red blood cells. A high or low result is a clue, not a diagnosis. A doctor reads it alongside haemoglobin, the rest of your full blood count, your symptoms and previous results before deciding whether anything needs checking.
What does MCV mean on a blood test?
MCV stands for mean corpuscular volume. It is usually included in a full blood count, sometimes called an FBC or CBC. Red blood cells carry oxygen around the body; MCV describes their average size rather than how many you have. MedlinePlus explains the test and its limits.
The useful question is not simply whether the number is highlighted. It is whether the result fits the rest of your blood count and whether it has changed. Your laboratory's reference interval is the starting point. A result outside it does not, on its own, establish a disease.
Ask the team about a doctor-led results review
What can a high MCV mean?
A raised MCV means the red blood cells are larger on average. The medical term is macrocytosis. Possible explanations include vitamin B12 or folate deficiency, alcohol, liver disease, certain medicines and an increase in newly produced red blood cells. Thyroid disease and, less commonly, bone-marrow conditions can also be relevant.
That list is not a way to diagnose yourself. BNSSG's haematology guidance recommends considering the history and other results, with tests such as B12, folate, a blood film, reticulocytes, liver function and thyroid function when appropriate. It also notes that sample storage or transport can affect a borderline result.
Do not stop a prescribed medicine because you think it may explain your MCV. Bring your medicines and supplements list to the review instead.
What can a low MCV mean?
A low MCV means the red blood cells are smaller on average. Iron deficiency is one possible cause. An inherited condition such as thalassaemia can also cause smaller cells. MCV cannot tell these apart by itself.
This matters because a low number is not an instruction to start iron. The doctor may need to check your iron status and the reason for any deficiency. Your symptoms, diet, periods, family history and other blood results help decide the next step. MedlinePlus describes iron-deficiency anaemia and thalassaemia among the possible causes of low MCV.
For a related result, read our guide to ferritin. Ferritin and MCV answer different questions and should not be treated as interchangeable.
Can I have anaemia with a normal MCV?
Yes. MCV measures cell size. It is not the same as haemoglobin, which helps establish whether you have anaemia. MedlinePlus notes that some types of anaemia occur with a normal MCV. A normal number therefore does not explain away tiredness or breathlessness, and an abnormal number does not automatically mean anaemia.
A useful review considers:
- Haemoglobin and the other red-cell measurements.
- White-cell and platelet results.
- Earlier blood counts and any change over time.
- Symptoms, medicines, alcohol intake and relevant medical history.
Do I need to repeat the test or have a larger panel?
Sometimes a repeat is useful. Sometimes the existing results already point towards a focused next test. Persistent unexplained changes, other abnormal blood-cell counts or a concerning blood film may need specialist advice, as set out in the BNSSG guidance.
Buying the largest panel is not the same as getting the right answer. Start with your full report and the question you want answered. A doctor can then explain what is worth repeating and what can be left alone.
View our doctor-led blood testing service, or ask about reviewing results you already have.
How much does a review cost?
As of October 2026, a telephone GP consultation is £59 and a video GP consultation is £150. Tell the team that you want to discuss a blood report so they can confirm the appropriate appointment and any proposed testing fees before you book.
Do I need to fast for an MCV blood test?
Not for MCV alone. Other tests taken at the same time may have preparation instructions. Follow the instructions for the whole request rather than fasting unnecessarily. This distinction is also made in the MedlinePlus test guide.
What should I bring to a results review?
Bring the complete report, including units and reference ranges, any earlier results, your medicines and supplements list, and a short account of your symptoms. A screenshot of MCV alone leaves out information the doctor may need.
For severe difficulty breathing, a tight or heavy chest, or collapse, call 999 rather than waiting for a routine results review.
Discuss your results with The Wellness team · Call 020 3951 3429 · Email the team
General information, not a diagnosis or a substitute for individual medical advice.