G-CSF causes decrease in peripheral blood platelet counts unrelated to leukapheresis during autologous stem cell mobilization

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Background & Aim Autologous transplant utilizing G-CSF mobilized peripheral blood stem cells (PBSC) is an established treatment for various conditions. PBSC collection has been reported to be associated with decrease in platelet counts, attributed to leukapheresis. Whether G-CSF directly affects platelet counts is unclear and studies show conflicting findings. We studied the change in platelet count, prior to start of leukapheresis, in patients receiving G-CSF for PBSC mobilization for autologous stem cell transplant Methods, Results & Conclusion Myeloma patients undergoing PBSC collection in our institution were retrospectively studied. Patients received 10 μg/kg G-CSF SQ daily. Stem cell collection started on day 4 (after 3 doses of G-CSF) if blood CD34 count on day 4 was at least 10 cells/μL (Good mobilizer). If not (Poor mobilizer), patients received plerixafor and another dose of G-CSF on day 4 followed by collection starting day 5. Complete blood count was measured before G-CSF on day 0 and on days 2,3,and 4 prior to start of leukapheresis. 163 patients were studied, median age 61 yr (39-74), 99(61%) were men. Platelet count (Mean ± SE) on day 0 was 230±5.9, which dropped to 192±4.4 (p We show a direct effect of G-CSF on platelet counts unrelated to leukapheresis. The decline is more severe in poor mobilizers. This together with known association of thrombocytopenia with poor mobilization, and expected further drop after leukapheresis is an important consideration when assessing safety and efficacy of G-CSF based mobilization in patient with low platelet count. The mechanism of G-CSF induced thrombocytopenia is likely multifactorial. Possibilities include G-CSF induced differentiation and proliferation of myeloid progenitors at the expense of megakaryocytic lineage, G-CSF induced activation and consumption (Platelets are known to have functional G-CSF receptors), or sequestration from G-CSF induced splenomegaly.