In order to prevent iron deficiency, Sanquin—the national blood bank in the Netherlands—measures a blood donor’s hemoglobin (Hb) level before each donation and only allows a donor to donate blood if their Hb is above a certain threshold. In around 6.5% of blood bank visits by women, the donor’s Hb is too low and the donor is deferred from donation. For visits by men, this occurs in 3.0% of cases. To reduce the deferral rate and keep donors healthy and motivated, we would like to identify donors that are at risk of having a low Hb level. To this end we have historical Hb trajectories at our disposal, i.e., time series consisting of Hb measurements recorded for individual donors.