RDW
Red Cell Distribution Width
- Sample
- Blood
- Usual units
- %
Also known as Red Cell Distribution Width · RDW-CV · RDW CV
What this test measures
Red cell distribution width describes how much red blood cell size varies within a single blood sample — a narrow spread means the cells are close to uniform in size, a wide one means sizes vary more. A lab reads it alongside MCV because the two together describe red blood cell size more completely than either alone. It is usually reported as a percentage.
Reading your report
There isn’t one standard range for this test — each lab prints its own. Use the range shown next to your result.
Related guides
- Guide
Why the same blood test has different "normal" ranges at different labs
Reference intervals are built from each lab's own population and equipment, which is why two labs can print different ranges for the same sample.
- Guide
Reference interval, cutoff, and the "optimal" numbers online: three different things
The range beside your result, the target a website quotes, and the threshold that defines a condition are built in different ways and answer different questions.
- Guide
Why the same lab printed a different reference range for you this year
Ranges are not fixed constants. The lab can change method, revise its reference group, or apply a range that depends on your age — none of which is an error.
- Guide
Haemoglobin, haematocrit and the red cell indices: MCV, MCH, MCHC, RDW
A blood count reports the same red cells several ways — a count, a protein, a percentage, and four averages computed from them. What each column is measuring.