Blood Health
RDW
What This Marker Tells Us
Measures the variation in red blood cell size, revealing whether your RBCs are uniformly sized or show significant size variation, which helps identify developing conditions before other markers change.
Why It Matters
RDW may be the earliest abnormality in developing iron deficiency. Normal RBC production creates uniformly sized cells; when RDW is elevated, it indicates your bone marrow is producing cells of varying sizes, typically because conditions are changing. In early iron deficiency, your bone marrow initially produces normal-sized cells, then gradually smaller cells as iron depletes, creating a mixed population and elevated RDW before MCV drops. Elevated RDW also correlates with inflammation, poor cardiovascular outcomes, mortality risk, and numerous chronic conditions. RDW provides early warning of iron deficiency, helps distinguish iron deficiency from thalassemia trait (high RDW vs. normal RDW), and serves as a general health marker.
How to Interpret Your Trends
Normal RDW is approximately 11.5-14.5%, representing minimal variation in cell size. RDW above 14.5% indicates increased variation (anisocytosis), suggesting developing iron deficiency, mixed nutritional deficiencies, recent bleeding with recovery, or chronic inflammation. RDW is often the first abnormal value in iron deficiency, rising before MCV drops. Very high RDW (above 18-20%) indicates severe anisocytosis from marked iron deficiency, B12/folate deficiency, or myelodysplastic syndrome. Thalassemia trait typically shows normal RDW despite low MCV, helping distinguish it from iron deficiency (high RDW with low MCV).
What Influences This Marker
RDW increases with iron deficiency (often first to change), B12 or folate deficiency (mixed cell sizes during treatment), chronic disease, inflammation, recent blood loss with regeneration (reticulocytosis), hemolysis, myelodysplastic syndrome, and general poor health or frailty. RDW correlates with cardiovascular disease risk, diabetes, chronic kidney disease, and all-cause mortality. RDW decreases (or remains normal) with thalassemia trait, chronic stable anemia, and states producing uniformly abnormal cells. Recent blood transfusion can temporarily normalize RDW.
How Your Team Uses It
Your coach implements strategies addressing identified deficiencies and emphasizing iron-rich foods with absorption enhancers when RDW elevation suggests iron depletion, or supporting anti-inflammatory dietary patterns when RDW reflects inflammatory burden.
Related Signals We Also Review
MCV, MCH, MCHC, ferritin, iron saturation, B12, folate, hs-CRP, and peripheral blood smear for complete evaluation of RBC abnormalities.