Red Cell Distribution Width: normal range and what it means
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
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Common questions
- What is a normal Red Cell Distribution Width level?
- Normal: < 14.5 %. Adult reference range.
- 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.