Red Cell Distribution Width (RDW)


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Subject: Red Cell Distribution Width (RDW)

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  • RDW is a coefficient of variation of the distribution of individual RBC volume.

  • Normal range: 12.1–14 fL.


  • An elevation in RDW is useful in drawing attention to anisocytosis, a marker for various anemias.


  • The RDW is particularly helpful in separating iron deficiency anemia (high RDW, normal to low MCV) from β-thalassemia trait (normal RDW, low MCV).

  • Increased RDW is also useful in identifying red cell fragmentation, agglutination, or dimorphic cell populations.


  • Very high WBC, numerous large platelets, and autoagglutination result in falsely elevated RDW.