Is my RDW (Red Cell Distribution Width) normal?
Free blood test checker · Standard + longevity-optimal ranges
What is a normal RDW level?
RDW measures the variation in red blood cell size (anisocytosis). Normal range is 11.5-14.5%, with a longevity optimal target of 11.7-13.0%. Elevated RDW reflects red blood cell size variability driven by inflammation, nutrient deficiency, or bone marrow stress. Beyond its traditional role in anemia classification, RDW is an independent predictor of biological aging and all-cause mortality — each 1% increase above 13% is associated with significantly increased mortality risk, even in people without anemia.
| Range | Values |
|---|---|
| Standard Reference | 11.5–14.5 % |
| Longevity Optimal | 11.7–13.0% |
| High Risk | > 17 % |
What causes abnormal RDW levels?
Elevated RDW is caused by iron deficiency (most common), B12 or folate deficiency, mixed nutritional deficiencies, chronic liver disease, chronic kidney disease, heart failure, chronic inflammation, myelodysplastic syndromes, recent blood transfusion (mixed donor/recipient cells), and hemoglobinopathies. Low RDW is generally not clinically significant.
When should you see a doctor?
See your doctor if RDW is above 14.5%, especially if combined with abnormal hemoglobin, MCV, or other CBC parameters. Even isolated elevated RDW with an otherwise normal CBC warrants nutritional screening (iron, B12, folate) and consideration of inflammatory markers.
RDW and longevity
Multiple large cohort studies have shown that RDW is one of the strongest independent predictors of all-cause mortality, even after adjusting for age, sex, and comorbidities. A 2019 JAMA study found that each 1% increase in RDW above 13% was associated with a 14% increase in mortality risk. This makes RDW a powerful, underappreciated marker for biological aging. The likely explanation is that RDW integrates multiple aging pathways: chronic inflammation, oxidative stress, nutritional status, and bone marrow function. Longevity-focused clinicians increasingly use RDW as an early warning signal — an elevated RDW in someone who "looks healthy" should trigger a deeper investigation into subclinical nutritional deficiencies and inflammatory processes.
Where to get a RDW test
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Related biomarkers
These biomarkers are often tested alongside RDW for a more complete picture.
Frequently asked questions
What is a normal RDW level?
Why is RDW linked to mortality?
Can I lower my RDW?
Why is RDW important for longevity?
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Sources: Reference ranges based on AHA/ACC, ADA, and AACE clinical guidelines. Biological variation data from Ricos/Westgard database. Longevity-optimal ranges reflect targets used by preventive and functional medicine practitioners.
Last reviewed: April 2026. This tool provides general health information and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider about your specific results.