Background: Collection of peripheral blood stem cells (PBSC) by leukapheresis has become the dominant method in allogeneic hematopoietic stem cell donation and also overpassed bone marrow donation in autologous transplantations. The circulating CD34 positive cells immediately prior to PBSC collection strongly correlate with the PBSC yield and have used to monitor donor's response to bone marrow mobilization. Methods:In this prospective study, a prediction method for PBSC collection that has been used in our facility was provided. Prediction accuracy is evaluated by comparison of predicted CD34 values to real PBSC yield. Results:The prediction method was used to determine first if a standard procedure with 12 L of blood processing could achieve the collection goal. Thirty seven donors were considered to have adequate PBSCs. Thirty four of them had a CD34 count above the target and only one donor had a CD34 count significantly below the target. For the donors whose PBSC were considered inadequate, an extended collection was performed based on the predicted blood volume that needed to be processed. The number of overestimated predictions was essentially the same as the number of underestimated predictions. Conclusion:The proposed prediction method was successful in identifying donors who needed extended collection without causing unnecessary prolongation of the leukapheresis procedure.