Red Cell Distribution Width (RDW) is a blood test parameter that assesses the variation in size and volume of a patient's red blood cells. A normal RDW value indicates a relatively uniform red blood cell population. The typical diameter of healthy red blood cells ranges approximately from 6 to 8 micrometers. Significant variations in this size can lead to an altered RDW value. Deviations from the established normal RDW range, whether lower or higher, can be indicative of underlying medical conditions.
For adults, the generally accepted normal RDW range typically falls between 11.5% and 14.5%, or sometimes cited as 12% to 15%. Specific reference intervals can vary slightly between laboratories and may also consider gender, with some sources indicating ranges like 12% to 16% for adult women and 11.8% to 14.5% for adult men. It is always essential to refer to the reference range provided by the specific laboratory performing the test for accurate interpretation.
RDW values outside the normal limits, whether abnormally low or high, can be associated with various conditions, including different types of anemia, vitamin deficiencies (such as iron, B12, or folate), inflammation, infection, or other systemic diseases. An abnormal RDW result therefore often necessitates further clinical evaluation.