Home › Lab markers › RDW (Red Cell Distribution Width)
COMPLETE BLOOD COUNT (CBC)
Also printed as: RDW · RDW-CV
Educational only — not medical advice.
RDW measures how much your red blood cells vary in size from one another. A low RDW means the cells are uniform; a higher one means there is a mix of smaller and larger cells. It says nothing about the average size — that is MCV's job.
RDW often shifts before the average does, which is why doctors find it useful early. It also helps separate causes that produce similar-looking MCVs.
TYPICAL ADULT RANGE
Many labs report roughly 11.5–14.5% for adults. Ranges vary by lab. Reported in %.
Reference ranges vary by lab, by method, and by age and sex. Always read your own result against the range printed on your report.
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A low or "normal-low" RDW simply means your red cells are consistently sized, which is not a problem and is generally not flagged. Most labs do not treat a low value as clinically meaningful. There is nothing to follow up on from this alone.
A higher RDW means a mix of cell sizes is circulating, which commonly happens when the body is transitioning — for example, early in a change in iron stores, when B12 or folate levels shift, or when new red cells are being produced after blood loss. Recent blood donation or a recent transfusion also raise it. It is a prompt for your doctor to look at ferritin, B12, and folate alongside MCV, and it is a common, routine follow-up rather than a worrying one.
Your doctor is the one who can read this number against your history, symptoms, and medications.
Educational only — not medical advice. Lab results only mean something alongside your history, symptoms, medications, and the rest of your panel. Bring questions to your doctor; they are the one who can interpret your results for you.
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