Red cell distribution width measures how much red blood cells vary in size within one sample — the spread around the average volume rather than the average itself. It is a measure of uniformity, and it tells whether the marrow is producing an even population of cells or several populations at once.
No readings for this marker yet.
Raised values most often appear when cells of different ages or different sizes circulate together: early iron, vitamin B12 or folate deficiency, recent blood loss, recovery after treatment of a deficiency, a recent transfusion, or ongoing hemolysis. Values are not usually low in a clinically meaningful way, and a normal spread does not exclude anemia. A widened spread is a prompt to look for a cause with a doctor, not a finding that stands alone.
A transfusion within recent weeks, an already-started iron or B12 supplement, and prolonged storage of the sample before analysis all shift the result. It is most useful next to MCV, since a widened spread with a small average is the usual pattern of existing iron deficiency and a widened spread with a large average points toward B12 or folate, and it is read alongside hemoglobin, hematocrit and MCH.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.