Lab test glossary · Blood count
MCV: what it means
Also known as: mean corpuscular volume, mean cell volume
MCV is the average size of your red blood cells — one of the most useful numbers for figuring out what's behind an anemia.
What it measures
MCV (mean corpuscular volume) is the average size of your red blood cells, reported as part of a CBC. Its real value is in classifying anemia: small cells (low MCV) point one way, large cells (high MCV) another — which narrows the search for a cause considerably.
Typical range
Often roughly 80–100 fL.
Reference ranges differ between labs and are printed on your own report — always read your result against that range, not a general one.
What a high result can mean
- Vitamin B12 or folate deficiency (large red cells)
- Alcohol use or liver disease
- Reduced thyroid function and some medications
A high value is a starting point for a conversation, not a diagnosis — many causes are benign or temporary.
What a low result can mean
- Iron deficiency (small red cells)
- Thalassemia, an inherited trait
Why the trend matters
A drifting MCV — even within the normal range — can be an early hint of a developing nutritional deficiency, which the trend catches before hemoglobin falls.
When to talk to your doctor
An MCV outside the range, especially with a low hemoglobin, is worth discussing with your doctor to pin down the type of anemia.
Frequently asked questions
What does a high MCV mean?
A high MCV means larger-than-average red blood cells, classically from vitamin B12 or folate deficiency, and also from alcohol, liver disease, or an underactive thyroid.
What does a low MCV mean?
A low MCV means smaller-than-average red cells, most commonly from iron deficiency or an inherited trait called thalassemia.
This page is general education about a common lab test — it isn’t medical advice and can’t interpret your specific result. What a value means depends on your history, symptoms, and the rest of your labs, which is a conversation for you and your clinician.