Effect of Exposure to Room Temperature During Storage on Cryopreserved Umbilical Cord Blood Quality

Cryopreserved umbilical cord blood (CB) for transplantation is occasionally exposed to room temperature during storage in cord blood banks. We evaluated the effect of room temperature exposure on the quality of cryopreserved CB. Forty frozen CB units stored in liquid nitrogen tanks were exposed to room temperature until they reached a target temperature of -130°C (group I), -60°C (group II), -40°C (group III), or -25°C (group IV) (N=10 in each group) and then re-stored. After re-thawing, the quality of the frozen CB was assessed based on the recovery rates of cell count, cell viability, and colony-forming unit granulocyte/macrophage (CFU-GM) content. The mean exposure times required to reach the target temperature were 0.83±0.14, 5.92±0.88, 10.28±1.0, and 16.0±1.62 mins for groups I-IV, respectively. CD34⁺ cell viability was significantly lower in group IV than in the other groups (P =0.009). The recovery rates of cell counts, cell viability except CD34⁺ cells, and CFU-GM did not significantly differ among the groups. Short-term exposure to room temperature for routine procedures and a temperature rise of up to -40°C during storage do not negatively affect the quality of cryopreserved CB.