Optimizing Timing of Peripheral Blood Stem Cell Collection: A Comparative Study of Day-4 Versus Day-5 Post-G-CSF Mobilization in Healthy Allogeneic Donors

Background and objectives: At King Hussein Cancer Center, peripheral blood stem cell (PBSC) collections in healthy allogeneic donors are typically initiated on day 4 of granulocyte colony-stimulating factor (G-CSF) mobilization, contingent upon circulating CD34+ cell counts (≥20 CD34+/µL). In cases where counts are suboptimal, collections are typically deferred to day 5. Research method: We conducted a retrospective cohort study on healthy allogeneic donors who underwent G-CSF mobilization and PBSC collection at KHCC between 2019 and 2023, comparing CD34+ dose on days 4 and 5 post G-CSF administration, to optimize collection timing, maximize yield, improve donor safety and institutional efficiency. The minimum cell dose considered acceptable for collection was set at 2.5 × 106 CD34+/kg. Continuous variables were summarized using the sample median and range. Categorical variables were summarized as numbers and percentages. CD34+ counts from days 4 and 5 were analyzed using a paired t-test. Statistical analysis was conducted using SPSS (version 29). Result and findings: We identified 526 donors during the study period: 326 (62%) donors collected on day 4 only, and 44 (8.4%) donors collected on day 5 only. This study focused on the remaining 156 (29.7%) donors who underwent collections on both days. For this group, the median age was 23 years (range 2–67 years), with 50.9% males. Median circulating CD34+/µL was lower on day 4: 48 (7–162) compared to day 5 was 75 (13–215). Mean cell dose collected (CD34+/kg) was significantly lower on day 4 compared to day 5 (4.4 × 106 vs. 6.1 × 106, respectively, p < 0.001), with 76% and 94% achieving an adequate collection dose on either day alone. In donors with a circulating CD34+ count <20 CD34+/µL on day 4, the likelihood of achieving an adequate cell dose was 30%, compared to 74% when the circulating CD34+ count was ≥20 CD34+/µL (p < 0.009). Conclusions: Peripheral CD34+ count on day 4 is a reliable predictor of stem cell yield. Delaying collection to day 5 in donors with suboptimal circulating CD34+ cells significantly improves yield and minimizing associated costs. These findings support evidence-based timing of collection to optimize donor outcomes and institutional efficiency in allogeneic PBSC mobilization.