Impact of non-transferrin-bound iron (NTBI) in comparison to serum ferritin on outcome after allogeneic stem cell transplantation (ASCT).

The optimal parameters and time points for the measurement of iron overload (IO) in allogeneic stem cell transplantation (ASCT) patients are still under discussion. Hyperferritinemia and IO are poor prognostic factors in ASCT. We hypothesize that non-transferrin-bound iron (NBTI) is possibly a better marker to predict the effect of IO on the outcome than serum ferritin (SF), which however is not specific for IO. The aim of this prospective observational trial was to evaluate the influence of NBTI in comparison to SF on the outcome of ASCT patients [overall survival, bloodstream infections (BSIs), and invasive fungal infections (IFIs)]. We analyzed daily transferrin saturation (TSAT), SF, and NTBI (if TSAT exceeded 70%) in 100 patients who received ASCT during conditioning, and on day 0, +7, and +14 post-ASCT. After a median NTBI level of 0 μmol/l at baseline, the median of the area under the curve (AUC) of NTBI between conditioning and ASCT (d0) increased to 17 μmol*d/l, and between ASCT and day +14 to 56.3 μmol*d/l. Higher NTBI-AUC d0 resulted in a higher risk of BSI (HR 1.042, p = 0.009) and IFI (HR 1.070, p = 0.001) and showed a trend of inferior 1-year survival (65 vs. 76%, p = 0.09). Baseline SF did not influence BSI, but higher levels resulted in more IFI (HR 1.26, p < 0.001). In conclusion, NTBI possibly better predict for a higher risk of bloodstream infections than SF and needs further investigation.