Mean cell volume is the average size of a red blood cell, derived from the red cell count and the hematocrit. It does not measure how much oxygen the blood carries; it describes what the cells look like. Its value is in sorting anemia into categories, which is why it is one of the first indices read when hemoglobin is low.
No readings for this marker yet.
A low mean cell volume, with small cells, most often points to iron deficiency and to thalassaemia traits. A high value, with large cells, most often points to vitamin B12 or folate deficiency, to alcohol use, to liver disease or hypothyroidism, and to certain medications; it can also rise when many young red cells are released after bleeding or haemolysis. A value inside the usual range does not exclude a deficiency, because mixed causes can cancel out. The category narrows the search rather than settling it, and the next step is a doctor.
Because it is an average, coexisting iron and B12 deficiency can leave it looking unremarkable while RDW rises, so the two are read together. Cyanocobalamin supplementation normalises a raised value over weeks and it is followed during treatment. It is interpreted alongside hemoglobin, MCH and MCHC, with reticulocytes and iron or B12 and folate studies following as the pattern suggests.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.