A, Mean hemoglobin for each group vs time since donation. Time “0” is the day of donation. B, Hemoglobin expressed as a percentage of initial hemoglobin value. Hemoglobin recovery was significantly higher than baseline in the low-ferritin group (≤26 ng/mL) who took iron (mean, 106.0%; 95% CI, 104.3%–107.7%; P < .001) and significantly lower than baseline in the higher-ferritin group (>26 ng/mL) who took no iron (mean, 98.1%; 95% CI, 96.6%–99.6%; P = .02). Dotted line indicates 100% of initial hemoglobin value; error bars, 95% confidence intervals.