Blood health
Red cell distribution width (RDW)
RDW-CV, RDW-SD
Included in every MyHealthspan membership: Focus, Baseline, and Complete.
Compare membershipsSpotting a mix of red cell sizes.
RDW measures how much your red blood cells differ in size from one another. It's read alongside MCV, the average cell size, to help work out the cause of anemia.
RDW adds a detail that averages can hide.
Your MCV is an average, and an average can look normal even when your cells are a mix of small and large. RDW shows that spread. A high RDW is common with low iron, vitamin B12, or folate.
Studies also link a higher RDW with heart disease, kidney and liver disease, and poorer outcomes in people with cardiovascular disease. Researchers are still working out what drives that link, so RDW is best treated as one input among many.
MCV gives the average size. RDW shows how much sizes vary.
Questions
Is a low RDW a problem?
A low RDW means your red cells are similar in size. It isn't a sign of anemia and usually isn't a concern.
What happens if my RDW is high?
Your iron, B12, and folate results often help explain a high RDW, along with your MCV and hemoglobin. A clinician can decide whether repeat testing or follow-up makes sense based on the full blood count and how you feel.
Sources and references