Summary:In all, 78 peripheral hematopoietic progenitor cell collections from 52 patients were evaluated using our previously published validated post-thaw assays at the time of collection and following transplantation by assessment of viable CD34 þ cells, and granulocytemacrophage colony-forming units (CFU-GM) cryopreserved in quality control vials. The median (range) post-thaw recovery of viable CD34 þ cells and CFU-GM was 66.4% (36.1-93.6%) and 63.0% (28.6-85.7%), respectively, which did not show significant correlation with the engraftment of either neutrophils (P ¼ 0.136 and 0.417, respectively) or platelets (P ¼ 0.88 and 0.126, respectively). However, the reinfused viable CD34 þ cells/ kg of patient weight pre-or post-cryopreservation showed significant correlation to engraftment of neutrophils (P ¼ 0.0001 and 0.001, respectively) and platelets (P ¼ 0.023 and 0.010, respectively), whereas CFU-GM pre-or post-cryopreservation was significantly correlated to neutrophils (P ¼ 0.011 and 0.007, respectively) but not to platelets (P ¼ 0.112 and 0.100, respectively). The results show that post-cryopreservation assessment of viable CD34 þ cells or CFU-GM is as reliable a predictor of rapid engraftment as that of pre-cryopreservation measures. Therefore, the post-cryopreservation number of viable CD34 þ cells or CFU-GM should be used to eliminate the risks of unforeseen cell loss that could occur during cryopreservation or long-term storage.