Test guide
RDW (Red Cell Distribution Width)
A red cell distribution width (RDW) test measures how much the volume and size of your red blood cells (erythrocytes) varies.
What it is for
The RDW blood test is often part of a complete blood count (CBC), a group of tests that measures the number and type of cells in your blood, including red cells. The RDW test is commonly used to help diagnose or determine what's causing anemia , a condition in which your body does not make enough red blood cells. The RDW test may also be used with other tests to help diagnose other conditions, including thalassemia , an inherited disease that can cause severe anemia. Source: MedlinePlus, National Library of Medicine. Medical test information is public domain. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Limitations
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also known as
- RDW-SD (standard deviation) test, Erythrocyte Distribution Width
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