Mean corpuscular volume: average red-cell size; helps classify anaemia patterns.
What it is
MCV is the average volume of red blood cells, reported in femtolitres (fL). It is calculated by automated counters as part of the FBC and is one of the main indices used to classify anaemia as microcytic, normocytic, or macrocytic.
Why it matters
Low MCV (microcytosis) often points toward iron deficiency or thalassaemia trait: haemoglobinopathy screens may be offered when appropriate. High MCV (macrocytosis) may relate to B12 or folate deficiency, alcohol, liver disease, hypothyroidism, or certain medicines.
MCV is most useful with haemoglobin, RDW, ferritin, and B12/folate. Mild shifts in a well person may simply be rechecked.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Red-cell size reflects marrow haemoglobinisation and DNA synthesis during maturation. Iron-restricted erythropoiesis produces smaller cells; impaired DNA synthesis produces larger ones. Mixed deficiencies can normalise MCV while RDW stays high.
For athletes
Athletes with falling performance and microcytosis often need iron stores checked, especially in endurance sport. Macrocytosis should still prompt alcohol, B12/folate, and medicine review, do not dismiss it as “sports anaemia” without data.
