Comparison of Peripheral Stem Cell Mobilization Results on the Fourth and Fifth Day of G‐CSF Treatment in Unrelated Donors

ABSTRACT Hematopoietic progenitor cell collection (HPC‐C) by apheresis after granulocyte‐colony stimulating factor (G‐CSF) stimulation is a routine worldwide procedure. The first apheresis procedure is typically performed on Day 5 of G‐CSF administration. We aimed to evaluate whether initiating the apheresis procedure on Day 4, with 1 day shorter G‐CSF exposure for the donor, affects collection outcomes. This study included healthy, unrelated donors who underwent HPC‐C by apheresis after G‐CSF administration between April 2022 and February 2024 at our center. Of 182 unrelated donors, 34.6% underwent apheresis on Day 4 of G‐CSF treatment and 65.4% on Day 5. There was no significant difference between the two groups in terms of collected CD34 + cell yield ( p = 0.369) or the need for a second apheresis procedure ( p = 0.74). Successful mobilization was achieved in 93.7% of donors who underwent a single apheresis procedure on Day 4 and in 95% of those who underwent a single apheresis procedure on Day 5 ( p = 0.477). In donors requiring two consecutive apheresis procedures, the collected CD34 + cell yield was higher in those who initiated apheresis on Day 4, although this difference was not statistically significant ( p = 0.067). This is the first study comparing HPC‐C outcomes on Days 4 and 5 of G‐CSF administration exclusively in unrelated donors. Our data indicate no difference in the collected CD34 + cell yield or the need for a second apheresis procedure between the two groups. Initiating apheresis on Day 4 may allow for 1 day less G‐CSF exposure without compromising collection outcomes.