Leukocyte and platelet counts can be used to guide collection of autologous stem cells after G-CSF mobilization on the first two days of leukapheresis but not beyond

We have shown recently that when healthy donors are treated with G-CSF to collect stem cells for allogeneic transplantation, the combination of a pre-apheresis leukocyte count of ≥25 x 109/L and a pre-apheresis platelet count of ≥100 x 109/L is associated with excellent mobilization as measured by an absolute peripheral blood CD34+ cell count (PBCD34) of ≥20/μL, and can be used to guide harvest timing (Tomblyn et al. Bone Marrow Transplantation advance online publication 01 August 2005; doi: 10.1038/sj.bmt.1705117 ). We wanted to see if this observation could be extended to patients receiving 10–16 μg/kg G-CSF daily as the sole mobilizing agent for autologous stem cell collection. Data from 161 leukapheresis procedures (65 day 1 collections, 47 day 2 collections, and 49 collections done beyond day 2) were analyzed to determine correlation between pre-apheresis leukocytes, platelets, and PBCD34. Overall, leukocytes (4.5–86.3; median 29.2) and platelets (26–452; median 121) correlated with PBCD34 (0.6–515.5; median 8.6); r=0.38 and 0.41 respectively (P<0.0001 for both). With leukocytes ≥25 and platelets ≥100, PBCD34 was 2.9–515.5 (median 31.8); significantly (P<0.0001) higher than PBCD34 of 0.6–226.0 (median 6.0) when leukocytes were <25 and/or platelets were <100. Among day 1 collections, with leukocytes ≥25 and platelets ≥100, PBCD34 was ≥20 in 63% of the time compared to 16% of the time if leukocytes were <25 and/or platelets were <100 (P=0.0001). On day 1, PBCD34 ≥10 was seen 78% of the time with leukocytes ≥25 and platelets ≥100, compared with 36% of the time with lower leukocyte or platelet counts (P=0.001). Similarly, PBCD34 levels of ≥20 and ≥10 were obtained 63% and 87% of the time with day 2 collections when leukocytes were ≥25 and platelets ≥100, compared with 19% and 35% of the time when leukocytes were <25 and/or platelets were <100 (P=0.003 and 0.001 respectively). For collections done beyond day 2, with leukocytes ≥25 and platelets ≥100, PBCD34 was ≥20 50% of the time compared with 7% when leukocytes were <25 and/or platelets were <100 (P=0.047). Beyond day 2, PBCD34 was ≥10 50% of the time with leukocytes ≥25 and platelets ≥100 compared with 8% of the time when leukocytes were <25 and/or platelets were <100 (P=0.18). Our data suggest that in patients with hematologic malignancies receiving G-CSF for mobilization of autologous stem cells, the combination of a leukocyte count of ≥25 and a platelet count of ≥100 is associated with excellent mobilization of stem cells as measured by PBCD34 in the majority of patients on the first and second harvest days. However, the relationship between good counts and PBCD34 is not as strong from the third day onwards, and a good leukocyte-platelet count combination is less powerful at predicting good mobilization. Conversely, lower leukocyte and/or platelet counts strongly predict for poor mobilization beyond the second day, but somewhat less strongly on the first two days. Thus, on the first and second days of stem cell collection in patients mobilized with G-CSF, apheresis can be initiated based on favorable hematologic parameters without necessarily awaiting PBCD34 levels. However, beyond the second day, PBCD34 levels should guide apheresis rather than surrogate markers such as leukocyte and platelet counts.