Red Cell Distribution Width: normal range and what it means
Short answer: The normal red cell distribution width range is < 14.5 % for adults. Labs differ a little, so also check the range printed on your report.
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Information, not a diagnosis. Talk to a doctor about your result, and sooner if you feel unwell.
Variation in red-cell size — high can be an early deficiency clue.
Normal range
Adult reference range.
- Normal< 14.5 %
- Borderline14.5 – 16 %
- High≥ 16 %
What it measures
How much your red cells vary in size. It often rises before haemoglobin falls, which makes it one of the earliest hints of a developing deficiency.
What moves it
Rises when red cells vary in size — typically early iron, B12 or folate deficiency, or a mix of causes. Often shifts before haemoglobin does, which is why it is worth noticing.
How to bring it into range
A raised RDW with a normal haemoglobin is a reason to check ferritin, B12 and folate now rather than at the next panel.
How fast it responds
Weeks to months.
Also reported as: rdw
Red Cell Distribution Width is one of nine markers in biological ageThe free PhenoAge calculator turns it and eight other routine results into your phenotypic age.See where your own value lands
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Common questions
- What is the normal red cell distribution width range?
- The normal red cell distribution width range is < 14.5 % for adults. Labs differ a little, so also check the range printed on your report.
- What does a high Red Cell Distribution Width mean?
- A value above the reference band means Red Cell Distribution Width is outside the range typical for a healthy adult. A single reading is rarely conclusive on its own — what matters is the trend across draws and the other markers around it, which is why HealthOS reads the whole panel together rather than one number at a time.
- How do I improve my Red Cell Distribution Width?
- A raised RDW with a normal haemoglobin is a reason to check ferritin, B12 and folate now rather than at the next panel.
More in Complete Blood Count
Reference ranges are general-population guidance compiled from common clinical laboratories, not a diagnosis. Lab-to-lab ranges differ. Always read your results with your doctor.