The RDW-to-RBC ratio is another calculation using red cell indices to help identify the possible cause of microcytosis.


RDW-to-RBC ratio =

=(RDW) / (RBC)



• RDW is the red cell distribution width

• red blood cell count is the number of red blood cells per µL, divided by 10^6



• iron deficiency: > 3.3

• thalassemia minor: < 3.3


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