IntroductionEffective mobilization of Stem Cells(SCs) to peripheral blood (PB) is crucial for obtaining sufficient CD34+ cell numbers via apheresis. The ratio of pre-apheresis PB CD34+ cells is the best parameter for predicting the product CD34+ cell count. However, quantitating CD34+ PB cells requires flow cytometry, which usually takes two or more hours to obtain the results. We hypothesized that the product CD34+ cell count could be predicted using the counts of white blood cells (WBCs), mononuclear cells (MNCs), and pre-apheresis CD34+ cells. A formula that achieves this would substantially affect the efficiency and effectiveness of apheresis. We, therefore, aimed to estimate the number of CD34+ cells in the product using a formula that incorporates pre-apheresis PB WBC, MNC, and CD34+ cell counts and product WBC and MNC counts. MethodsWe examined the results of 373 leukapheresis procedures for SC mobilization. Effective separation of CD34+ PBSCs (count/μL) via apheresis was estimated using the following formula: [Product WBC (count/μL) × MNC (count/μL) × pre-apheresis CD34+ cell (percentage/μL)] ÷ [PB WBC count/μL × PB MNC (count/μL)]. ResultsA strong correlation was observed between the CD34+ cell count calculated using our formula and the post-apheresis CD34+ cell count measured via flow cytometry (R = 0.939, based on linear regression analysis). In the subgroup analysis, this correlation was observed for all the disease subgroups and healthy donors. ConclusionWe developed a formula that predicts the product CD34+ cell count and is useful for determining whether a second apheresis procedure will be required.