Not medically reviewed
Haematology
Red cell distribution width (RDW)
Not medically reviewed · Content last updated · 1 min read ·
This is the date the draft was written, not a medical review date.
RDW quantifies variation in red-cell size (anisocytosis), usually as the coefficient of variation of the volume distribution.
Reference interval
| Conventional (%) | SI (%) | |
|---|---|---|
| Adults | 11.5–14.5 % | 11.5–14.5 % |
Specimen: Whole blood (EDTA) · Conventional × 1 = SI
Causes of high values
Iron, B12 or folate deficiency (including mixed deficiencies), haemolysis with reticulocytosis, recent transfusion, myelodysplasia and haemoglobinopathies.
Causes of low values
A low RDW has little clinical significance.
Pre-analytical and method notes
Two forms exist (RDW-CV, usually 11.5-14.5 %, and RDW-SD in fL); reference limits depend on the analyser. A raised RDW with normal MCV may be an early sign of nutritional deficiency or a mixed picture.
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
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