Red cell distribution width (RDW) is a red blood cell parameter that measures variability of red cell volume/size (anisocytosis). Depending on the types of 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. The average RBC size therefore has no effect on this parameter and you get MCV or mean corpuscular volume.
RDW-CV is expressed in percentage and is calculated from MCV and standard deviation.
The reference range for RDW is as follows:
RDW-SD 39-46 fL
RDW-CV 11.6-14.6% in adult
Reference ranges may vary depending on the individual laboratory and patient’s age.
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