Red Cell Distribution Width, Revisited

The red blood cell distribution width (RDW), as part of an automated complete blood count (CBC), is a routinely available parameter on hematology analyzers. This parameter is the most commonly reported index of the variation in red cell volume and can be used to detect subtle degrees of anisocytosis. It is one of the most studied parameters; however, some earlier studies have shown overlap or discrepancy in the interpretations of these results. RDW is computed directly from the red blood cell (RBC) histogram and expressed as coefficient of variation (CV) or standard deviation (SD). In conjunction with other CBC parameters, such as the histogram, mean corpuscular volume (MCV), and peripheral blood film analysis, RDW is frequently used to interpret aberrations in red cell morphology. This article describes and discusses the different methods for measuring red blood cell dispersion and explains the reasons for the inconsistencies observed when interpreting RDW results.