RDW (Red Cell Distribution Width) shows how much your red blood cells vary in size. A high RDW means a mix of small and large cells.
- Normal range (adults)
- 11.5–14.5%
- Sample
- Blood
- Fasting
- Not usually needed
- Also called
- Red Cell Distribution Width, RDW-CV, RDW-SD, Red Blood Cell Distribution Width
RDW normal range
| Group | %Same unit in all countries |
|---|---|
| Adults | 11.5–14.5 |
Ranges vary slightly between laboratories. The range printed on your own report is the one to go by.
Why is the RDW test done?
It is part of the Complete Blood Count and helps tell types of anemia apart, often before hemoglobin drops.
What does a high RDW level mean?
A high RDW means your red cells vary a lot in size, which often happens early in a nutrient deficiency or when two causes of anemia are present.
Common causes
- Early iron deficiency
- Vitamin B12 or folate deficiency
- Mixed deficiencies
- Recent blood loss or transfusion
- Liver disease
Diet and lifestyle tips
- Eat iron-rich foods with vitamin C
- Include B12 and folate sources
- Check iron, B12 and folate levels before starting supplements
When should you see a doctor?
A high RDW on its own is not dangerous, but your doctor may order ferritin, B12 or folate tests to find the cause.
Last updated
This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.