Serum GDF15 is increased by DFO treatment in vivo. Eight persons were infused with saline or 4 g/70 kg DFO for 8 hours on 2 separate days. On each day, blood was taken from each person at the start of the infusion (t = 0 hours), 4 hours into the infusion (t = 4 hours), at the end of the infusion (t = 8 hours), and 4 and 16 hours after the end of the infusion (t = 12 hours and t = 24 hours, respectively). Serum samples were stored at −20°C for use in ELISA. (A) Serum concentration of GDF15 in saline and DFO treatment were measured by ELISA. Data for each time point are plotted as the mean plus or minus SE of GDF15 serum levels in all 8 persons. Mann-Whitney test was used to calculate the significance of difference between GDF15 levels in DFO and saline infusions at t = 8 hours and t = 12 hours. (B,C) Fold change in GDF15 serum concentration over time was calculated relative to time t = 0 in all 8 DFO- and saline-treated persons. Plotted data are the means of duplicate ELISA measurements.