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Background: Cord blood (CB) is a product rich in primitive adult stem cells used in hematopoietic stem cell transplantation. After collection, the CB is transported to a facility where the unit is processed and then frozen up to 48 hours later. These processes can lead to compromised white blood cell (WBC) viability. This study investigates the factors that affect WBC viability before freezing of the cells., Study Design and Methods: We retrospectively analyzed WBC viability from 9918 CB collections harvested from 2003 to 2010 to determine if collection volume and time to freezing (TTF) had a significant effect on WBC viability. CB was collected in dispersed clinical locations by local staff trained to the same methods. CB was transported to the central lab under controlled conditions for analysis and processing., Results: The collected CB units had a mean volume of 77.1 ± 31.3 mL, mean WBC count of 10.5 × 10(8)  ± 5.6 × 10(8) , mean total CD34+ cell count of 4.0 × 10(6)  ± 3.7 × 10(6) , and mean WBC viability of 91.7% ± 6.5%. WBC viability was most significantly affected by the volume of CB collected and the TTF. As collection volumes increased, WBC viability increased, with mean viability of 95.0% ± 3.5% in CB collections of more than 120 mL. Decreased viability was associated with volumes of less than 60 mL and TTF of more than 24 hours. From these data we have developed decision tables that estimate WBC viability based on CB volume and TTF., Conclusion: This study identifies optimal TTF for different collection volumes to maintain WBC viability of the collected CB., (© 2011 American Association of Blood Banks.)