The Effect of Long-Term −80°C Storage of Thyroid Biospecimens on RNA Quality and Ensuring Fitness for Purpose

Aims To establish whether RNA degrades in long-term storage at −80°C and whether RNA integrity numbers (RINs) determine ‘fitness for purpose’ in severely degraded RNA. Methods RNA was extracted from 549 thyroid biospecimens stored at −80°C for 0.1–10.9 years then their RINs correlated with storage time. RT-PCR for 65, 265, 534 and 942 base pair amplicons of hydroxymethylbilane synthase was used to measure amplicon length in RNA from cryopreserved and FFPE biospecimens that were equally degraded according to RIN. Results Storage time did not correlate with RIN. Longer amplicons were obtained from cryopreserved samples than FFPE samples with equal RINs. Conclusions RNA does not degrade in thyroid biospecimens stored for long periods of time at −80°C. Although RINs are known to predict amenability to analytical platforms in good quality samples, this prediction is unreliable in severely degraded samples.