Red Blood Cell Distribution Width (RDW): Definition and Calculation

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The page below is a sample from the LabCE course Describing a Red Blood Cell Population Using RBC Indices and Red Cell Distribution Width. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Red Blood Cell Distribution Width (RDW): Definition and Calculation

The red cell distribution width (RDW) is derived from the red blood cell distribution curves generated on automated hematology analyzers. It indicates variation in RBC size within a blood sample. The RDW is used along with the indices (MCV, MCH, MCHC) to describe a population of RBCs. The RDW measures the deviation of the RBC width, not the actual width or size of individual cells.
The two RDW measurements currently used are the red cell distribution width coefficient of variation (RDW-CV) and the red cell distribution width standard deviation (RDW-SD).