RDW (RDW-CV)

Red Cell Distribution Width (RDW or RDW-CV) measures the variation in the size of red blood cells (anisocytosis), reported as a percentage coefficient of variation. A high RDW indicates a large variation in cell sizes, commonly seen early in iron deficiency anemia (mix of small and normal cells) and B12/folate deficiency (mix of large and normal cells), often before MCV changes. Consistently low RDW (<13%) is generally considered optimal, indicating uniform cell size.