MCV
Mean Cell Volume
What this test measures
MCV measures the average size of your red blood cells. It helps identify the type of anaemia you might have. Small cells often mean iron deficiency; large cells can indicate B12 or folate deficiency.
Understanding the numbers
Typical range: 80-100 fL
MCV is most useful when interpreted alongside haemoglobin and other blood count results.
- Microcytic (small): 60–80 fL
- Normal: 80–100 fL
- Macrocytic (large): 100–120 fL
Key numbers
- 80 fL — Below = think iron deficiency or thalassaemia
- 100 fL — Above = think B12/folate/alcohol/thyroid
Typical UK reference range. MCV is directional — the value itself matters less than what it points you towards. Interpreted alongside haemoglobin, ferritin, B12, folate, TFTs and alcohol history.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean (Large cells)
- Your red blood cells are larger than normal
- Often caused by vitamin B12 or folate deficiency
- Alcohol excess is a common cause
- Some medicines and thyroid problems can also cause this
Questions you could ask your GP
- What is causing my abnormal MCV?
- Do I need tests for iron, B12, or folate?
- Could this be related to my diet or alcohol intake?
- Should I be tested for thalassaemia?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Low MCV, small cells, iron deficiency
Ahana's MCV was 72 fL and her haemoglobin was 102 g/L. Ferritin was 5 µg/L. She had heavy periods.
What the GP said: “Small red cells and low ferritin together point clearly to iron deficiency anaemia. We'll start iron tablets and sort out the heavy periods.”
What happened next: After six months on iron and a tranexamic acid plan for periods, Ahana's MCV was 88 and haemoglobin 128.
A low MCV is the blood count's clearest pointer towards iron deficiency — it responds well to treating both the deficiency and the cause.
High MCV, drinks most days
Danny's MCV was 106 fL but his haemoglobin was 142. His B12 and folate were normal, his TFTs were normal, and he drank around 30 units a week.
What the GP said: “Alcohol is the most likely cause of the large cells. Cutting down should bring it back. Let's aim for under 14 units a week and recheck in three months.”
What happened next: Danny cut down to 8 units a week. His MCV was 94 fL at the next check.
A high MCV without anaemia is often the first sign of alcohol excess. It's a non-judgemental conversation-starter that can lead to real change.
High MCV and anaemia — B12 deficiency
Nilima's MCV was 112 fL and haemoglobin 96 g/L. Her B12 was 78 pmol/L, folate normal, and intrinsic factor antibodies positive.
What the GP said: “This is pernicious anaemia — an autoimmune cause of B12 deficiency. Treatment is hydroxocobalamin injections, loading doses first, then every three months for life.”
What happened next: After loading injections Nilima's MCV was 92 and haemoglobin 130 at three months.
A high MCV with anaemia should always trigger B12 and folate testing. Pernicious anaemia is permanent but very manageable with injections.
Low MCV but not iron deficient
Tejas's MCV was 68 fL with a haemoglobin of 135. His ferritin was 120 — not low. Both parents were from South Asia.
What the GP said: “This looks like thalassaemia trait — an inherited condition that makes red cells smaller but doesn't usually cause anaemia. A haemoglobin electrophoresis will confirm it. Important to know if you're planning children.”
What happened next: Thalassaemia trait was confirmed. Tejas and his partner were both screened before pregnancy.
A persistently low MCV with normal iron stores suggests thalassaemia trait — common in people of South Asian, Mediterranean or African background. It's not an illness for the carrier, but matters for family planning.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.