What Is the Definition of RDW-SD?

What is the definition of RDW-SD?

Red cell distribution width (RDW) is a red blood cell parameter that measures variability of red cell volume/size (anisocytosis). According to different types of the hematology analyzer instruments, RDW can be reported statistically as coefficient of variation (CV) and/or standard deviation (SD), RDW-CV and/or RDW-SD, respectively.

RDW-SD takes measurements in “fL” and basically measures the width of red cells size distribution histogram–it calculates the width at the 20% height level of the histogram.

Here is a chart providing the clearer visual explanation.

The normal range of RDW-SD is 39-46 fL.

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