RDW (Red Cell Distribution Width) Test
The RDW test measures how much the size of your red blood cells varies. A high RDW means your red blood cells are more varied in size than normal, which may be a sign of certain health conditions. A low RDW means your red blood cells are similar in size, which is usually not a concern.
What this test measures
A red cell distribution width (RDW) test measures how much the volume and size of your red blood cells varies.
What your results mean
Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.
Higher-than-normal results
A high RDW result may be a sign of conditions such as chronic liver disease, heart disease, diabetes, kidney disease, or cancer (especially colorectal cancer).
Lower-than-normal results
A low RDW result is not a sign of anemia and isn't usually something to worry about.
Frequently asked questions
What does RDW stand for?
RDW stands for Red Cell Distribution Width.
Is the RDW test part of a complete blood count?
Yes, the RDW blood test is often part of a complete blood count (CBC).
What does a high RDW result mean?
A high RDW result means your red blood cells vary in size more than normal, which may be a sign of certain conditions like chronic liver disease, heart disease, diabetes, kidney disease, or cancer.
What does a low RDW result mean?
A low RDW result means your red blood cells are similar in size and is not a sign of anemia. It is usually not something to worry about.
Can I have anemia even if my RDW is normal?
Yes, even if your RDW results are normal, you may still have anemia or another medical condition that may need treatment.
Related lab tests
Sources
- MedlinePlus: RDW (Red Cell Distribution Width) — NIH MedlinePlus
Last updated . Information is aggregated from official public sources and is not a substitute for professional medical care.