What Is a RDW Blood Test? An RDW blood test – also known as a red blood cell distribution width blood test – is a measure of the difference in your red blood cells’ size and volume. RDW is one part of ...

The red cell distribution width (RDW) blood test measures differences in the volume and size of your red blood cells. Red blood cells help carry oxygen from the lungs to other parts of your body.

Red blood cells transport oxygen throughout your body, including to vital organs and tissues. They also help your body get rid of carbon dioxide. Too little or too many red blood cells may be ...