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

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.