Red Cell Distribution Width (RDW)

Red Blood Cell Distribution Width (RDW) measures the variation in the size (volume) of red blood cells (erythrocytes) and is routinely reported as part of the CBC. An RDW test uses a histogram, a type of graph where red blood cells of a similar size cluster closely, resulting in a low RDW. Conversely, a high RDW indicates greater variability in cell size, and a wider spread on the histogram. Clinically, elevated RDW values may indicate underlying health conditions such as nutritional deficiencies, bone marrow disorders, or other systemic diseases. RDW values are interpreted alongside other blood indices to support risk assessment. [76]

[76]El Brihi J, Pathak S. Normal and Abnormal Complete Blood Count With Differential. In: StatPearls. StatPearls Publishing; 2025. Accessed November 6, 2025. http://www.ncbi.nlm.nih.gov/books/NBK604207/

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