Serum ERFE and hepcidin after blood donation. (A) Serum ERFE in blood donors of 2 units of erythrocytes. Colored lines denote individual donors. Red and blue circles and error bars show mean ± standard error of the mean for each time point. Red denotes P < .05 by 1-way repeated measures analysis of variance (ANOVA) compared with initial baseline (day 0) concentration. The first postdonation sample was obtained at average 2.5 days after donation (range 2-4 days) and showed an increase in all samples, by 16.4 ± 8.9 ng/mL over initial sample (mean increase ± SD, P = .0002, paired Student t test, n = 24). Further rise of serum ERFE was seen in most donors with a maximum at 8 ± 4 days (mean ± SD, n = 24) increasing by 26.7 ± 11.2 ng/mL over initial value. By 112 days after the blood donation, serum ERFE concentrations returned to baseline (3.9 ± 7.5 ng/mL over initial, P = .28 comparing baseline and 112 days, paired Student t test, n = 20). (B) Serum hepcidin in the same donors is shown for reference. Red denotes P < .05 by 1-way repeated measures ANOVA compared with initial baseline (day 0) concentration.