Red Cell Distribution Width

When elevated (>15% -- increased RBC size variation):

Common causes in AAS users:

• Early iron depletion -- New iron-deficient cells are smaller while older normal cells persist, increasing size variation. RDW rises before MCV drops, making it an early warning of iron depletion.
• Mixed deficiency -- Simultaneous iron deficiency (small cells) and B12/folate deficiency (large cells) produces a wide size distribution with normal MCV.
• Post-blood donation -- Accelerated new cell production alongside older cells increases variation.

Supplements:

• Iron Bisglycinate -- 25-50mg/day with Vitamin C 500mg (if Ferritin <50 ug/L)
• Vitamin B12 (Methylcobalamin) -- 1000mcg/day (if B12 borderline/low)
• Methylfolate -- 800mcg/day (if Folate borderline/low)

Follow-up:

• Check Ferritin, B12, and Folate to identify the deficiency driving the elevation
• A high RDW with normal MCV and normal Ferritin may indicate B12/folate deficiency even before MCV rises
• RDW normalises as the underlying deficiency is corrected (8-12 weeks)

References:

• Camaschella, C. (2015). Iron-deficiency anemia. New England Journal of Medicine, 372(19), 1832-1843. DOI: 10.1056/NEJMra1401038
• Stabler, S. P. (2013). Vitamin B12 deficiency. New England Journal of Medicine, 368(2), 149-160. DOI: 10.1056/NEJMcp1113996
• Bailey, L. B., & Gregory, J. F., III. (1999). Folate metabolism and requirements. Journal of Nutrition, 129(4), 779-782. DOI: 10.1093/jn/129.4.779