Presence of enhanced labile plasma iron in sera of patients undergoing allogeneic hematopoietic stem cell transplantation determines AFU outgrowth. Human serum samples of 29 representative ALLIVE participants, which were collected during the consecutive phases of allogeneic hematopoietic stem cell transplantation (HSCT) were screened for AFU outgrowth. AFU spores (5 × 10⁴/mL) were seeded in RPMI containing 10% complement-depleted patient serum. Outgrowth was determined after 48 hours by microscopic examination. (A) Microscopy images showing fungal cultures of a representative patient (DD-15) with eLPI serum concentrations as indicated (original magnification ×20; bars represent 30 µm). (B) Heat map representation of fungal outgrowth (upper left), eLPI presence (lower), and their overlay (right) of patients analyzed here at all times (green, fungal outgrowth; red, eLPI present; yellow, both fungal outgrowth and eLPI present; gray, fungal growth and eLPI absent; white, sample not available). (C) Relative probability of AFU outgrowth in sera of patients depending on iron-related parameters (eLPI concentration, eLPI presence, Tf-Sat, and Tf-Sat > 75%. The graph depicts ORs ± 95% CIs for probability of fungal outgrowth. Statistical significance was assessed using a multiparameter logistic regression model for the outgrowth response variable (no fungal growth vs fungal outgrowth). 0, day of transplantation; 7-100, days 7-100 after transplantation; BL, baseline; C1-7, conditioning days 1-7.