Background: Parathyroid cryopreservation is used for potential autografting in patients who are rendered hypocalcemic following surgery. Cryopreservation employs multiple resources and carries a significant cost for processing and storage of tissue. Importantly, the length of time that parathyroid tissue remains functional after cryopreservation is not known. The goal of our study was to assess ex-vivo viability of parathyroid tissue in relation to the length of time in storage. We sought to define the appropriate time frame for tissue utilization and disposal to assist with long-term surgical planning. Methods: From 1991 to 2006, 501 parathyroid specimens from 149 patients were cryopreserved at -80°C according to standardized techniques. A single trained technician assessed viability, using a hemacytometer to count viable (clear cell) and nonviable (blue cell) tissue. Univariate analysis was performed to correlate length of preservation, diagnosis with viability. Results: We evaluated 106 random parathyroid specimens. Samples were divided into two groups: those stored > 24 months and those stored ≤ 24 months. Eleven (10%) of 106 specimens were deemed viable. Length of storage time was associated with ex-vivo tissue viability. Viability of samples cryopreserved ≤ 24 months was 71% (10/14) versus 1% (1/92) of those specimens stored > 24 months (p < 0.001). Conclusions: Viability of cryopreserved parathyroid cells is associated with duration of storage. Parathyroids preserved for greater than 24 months are unlikely to be viable. It seems reasonable to limit parathyroid cryopreservation to 24 months when frozen at -80°C. Further studies are needed to optimize the process of cryopreservation to enhance cell viability.
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