Iron and blood status
What is RDW?
variation in red cell size
- Unit
- %
- Sample
- Whole blood
- Fasting
- No fasting needed
- Turnaround
- 1 day
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.
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
- Performance Test Base
- Performance Test Plus
- Health Check Plus
- Iron Test Complete
- Performance Test Complete
- Health Check Complete
- Health Check Man
- Health Check Kvinna
More markers in the same area
Launching in Stockholm in 2026.
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This is general information about the marker, not an assessment of your values and not medical advice. Last updated: August 2026.