What is RDW?
variation in red cell size
RDW measures how uniform or varied red cell sizes are. It helps clarify the cause of an anaemia.
A high RDW means red cells vary widely in size. This can be an early sign of iron deficiency before MCV drops, making RDW useful in early diagnosis.
Test facts
- Unit
- %
- Sample
- Whole blood
- Fasting
- No fasting needed
- Turnaround
- 1 day
What does low RDW mean?
A low RDW is not clinically significant.
What does high RDW mean?
High RDW often appears with iron deficiency, B12 deficiency, mixed nutritional deficiency, and certain chronic illnesses.
Panels that measure RDW
- Deep Baseline
More markers in the same area
Launching in Stockholm in 2026.
Want to know when you can order?
This is general information about the marker, not an assessment of your values and not medical advice. Last updated: May 2026.