Red Cell Distribution Width (RDW)
- Sample Type
- Standard
- Fasting
- No
- Unit
- %
RDW is a numerical measure of anisocytosis, or the variation in size of circulating red blood cells (RBCs). In a healthy individual, RBCs are relatively uniform in size. A high RDW indicates a wide range of cell sizes (small, normal, and large). In the context of a CBC, RDW is invaluable for differentiating between types of microcytic anemia; for example, Iron Deficiency Anemia typically shows a high RDW, whereas Thalassemia minor often presents with a normal RDW despite low MCV.
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Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
A recent blood transfusion can cause a temporary, significant increase in RDW as the recipient's blood mixes with the donor's cells. High RDW is also a non-specific marker of general inflammatory stress and can be elevated in cardiovascular disease without primary hematologic pathology.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Red Cell Distribution Width (RDW):
Official Sources
Research & Guidelines
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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