RDW
Also reported as: Red cell distribution width · RDW-CV
How much red blood cells vary in size. A low value means a uniform population; a high one means the marrow is producing cells of inconsistent size.
The upper bound sits well above where risk associations begin.
Cohort data show mortality risk rising from around 13%, comfortably inside the reference range, and continuing to climb across it.
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Where the thresholds sit
| Band | Range (%) | Note |
|---|---|---|
| Optimal | < 13 | — |
| Acceptable | 13–14 | — |
| Borderline | 14–14.5 | — |
| Elevated | > 14.5 | Check iron, B12, folate and inflammatory markers. |
Why it matters
Almost nobody looks at it, and it is one of the strongest mortality predictors hiding on a standard full blood count. Raised RDW predicts all-cause mortality, cardiovascular events and cancer outcomes independently of haemoglobin and of every other cell index — probably because it integrates inflammation, oxidative stress and nutritional status into one number. It costs nothing extra; it is already on the test you have had.
What raises it
- Iron, B12 or folate deficiency — the commonest and most fixable causes
- Chronic inflammation
- Liver disease
- Recent blood transfusion
- Alcohol excess
What lowers it
- Correcting the underlying deficiency
- Resolving the inflammatory driver
How to move it
- 1Treat a raised RDW as a prompt to check ferritin, B12 and folate. A nutritional cause is the most likely and the most correctable.
- 2Check hs-CRP too — inflammation raises RDW independently of any deficiency.
- 3Reduce alcohol.
- 4Retest after 8-12 weeks; red cells take that long to turn over.
What moves this marker
Interventions on this site with evidence behind them for this specific marker. None of them replaces working out why yours is where it is.
What makes a single reading misleading
- Entirely non-specific. It tells you something is disturbing red cell production, not what.
- Rises transiently after a transfusion or a bleed.
- Interpret alongside MCV and haemoglobin rather than alone.
Sources
Read next
Educational only. Reference ranges are not diagnostic thresholds and this page cannot account for your medical history, medication or symptoms. Discuss any result that concerns you with a qualified clinician. See our medical disclaimer.