Red cell distribution width (RDW-CV)
Blood cell systemAlso known as: RDW coefficient of variation, red cell distribution width CV, Erythrozyten-Verteilungsbreite
Red Cell Distribution Width (Coefficient of Variation) measures the variation in red blood cell size.
Elevated values indicate greater variation in cell size (anisocytosis) and can help diagnose certain anemias.
Reference range
Female
Source: lab benchmark
Male
Source: lab benchmark
Reference ranges may vary between labs and assays. Always interpret results with your healthcare provider.
Why this matters
RD-CV (Red Cell Distribution Width – Coefficient of Variation) reveals early changes in red blood cell production before anemia symptoms appear. High RD-CV may indicate nutrient deficiencies (like iron, B12, or folate), chronic inflammation, or bone marrow disorders. Identifying abnormalities early allows dietary adjustments, supplementation, or medical evaluation to prevent anemia and support healthy blood function.
How this connects to other biomarkers
- Elevated RDW indicates a mix of large and small red cells and can precede overt anemia; combined with low MCV it is the earliest hematologic signal of evolving iron deficiency.
- High RDW with macrocytic anemia (high MCV) is classic for Vitamin B12 / Folic acid (Vitamin B9) deficiency.
- Elevated RDW alone is independently associated with cardiovascular and all-cause mortality, even with normal Hemoglobin — it may reflect underlying chronic disease or oxidative stress.
How often should I test Red cell distribution width (RDW-CV)?
Most adults benefit from yearly RDW-CV testing as part of a complete blood count. When investigating anemia or supplementing iron, B12, or folate, retest at 3 months.
At baseline / for screening: Once every 12 months from age 30 as part of a comprehensive panel.
When monitoring an intervention or change: Retest 4 to 8 weeks after starting iron, B12, or folate supplementation for anemia, or after blood loss recovery. Red blood cells take about 120 days to fully turn over, so meaningful changes in cell size and content (MCV, MCH) take 3 to 4 months. Hydration on the morning of the draw shifts concentration-based measures, so reproduce conditions for reliable trends.
Note: RDW rises early in evolving iron, B12, or folate deficiency, often before MCV becomes abnormal. After starting supplementation, RDW transiently widens further over 4 to 8 weeks (new healthy cells joining older smaller cells) before normalizing over 3 to 4 months.
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