RDW
A measure of how much red blood cells vary in size.
| Typical reference range | 11–15 % |
| Commonly cited optimal range | below 13.5 % |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
Red cell distribution width expresses the variation in red cell volume. A high RDW means a mix of small and large cells (anisocytosis).
Why it matters
RDW often rises early in iron, B12 or folate deficiency, before MCV changes. Elevated RDW is also independently associated with cardiovascular disease, inflammation and mortality.
What a high result can mean
High RDW occurs with iron, B12 or folate deficiency, mixed deficiencies, recent blood loss or transfusion, hemolysis, recovery from anemia, liver disease and chronic inflammation.
What a low result can mean
Low RDW is not clinically significant.
What affects the result
Some labs report RDW-SD in fL instead of RDW-CV in %; these are not interchangeable. Interpret with MCV and iron, B12 and folate status.
Unit
Usually reported in %.
Also called on lab reports
RDW-CV, Red Cell Distribution Width, Red Blood Cell Distribution Width, RDW CV
Related tests: Red Blood Cells
This page is educational and does not replace advice from a healthcare professional.