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RDW (Red Cell Distribution Width) measures the variability in red blood cell size — a high RDW means your cells vary widely in size (anisocytosis), which is an early sign of nutritional deficiency or mixed anaemia. RDW rises early in iron, B12, and folate deficiency, often before haemoglobin drops to anaemic levels, making it a sensitive early-warning marker. A high RDW is also an independent predictor of cardiovascular mortality, infection severity, and all-cause mortality — reflecting underlying systemic inflammation and nutrient deficiency.
Also known as: RDW, RDW-CV, RDW-SD, Red Blood Cell Distribution Width, Red Cell Distribution Width
High RDW means your red blood cells vary widely in size, an early signal of iron, B12, or folate deficiency before MCV or hemoglobin shifts. Elevated RDW also independently predicts cardiovascular mortality. Low RDW is normal.
Standard range is 11.5-14.5%. Functional targets are 11.5-13.0%. RDW above 13% even with normal hemoglobin should trigger ferritin, B12, and folate testing.