how long can samples be stored before testing?
How long can a biological sample be stored before testing? It’s a complicated question. Answers are generally speculative and depend on a variety of factors.
Of what quality is the sample in question? For which analytes are you testing? If pre-analytical variables are controlled according to the best practices and quality assurance standards, and proper storage protocols are developed, some biosamples can be stored for years.
Human Tissue Samples
According to a 2016 study of the thyroid tumor samples from the Chernobyl Tissue Bank, tumor samples can, regarding RNA integrity, be stored at -80°C without degradation for at least eleven years. These findings are supplemented by the results of a study of 153 adrenal tissue samples (normal adrenal gland and various adrenal tumor tissues) stored at -80°C for up to 27 years. Samples exhibited an ‘‘acceptable’’ or ‘‘excellent’’ tissue morphology, with no correlation between the quality of RNA and time of storage. Similarly, RNA quality did not degrade in liver tissue samples after seven years at -80°C and -150°C; neither in brain autopsy tissue samples stored at -70°C for 15 years.
According to a long-term biobanking research of urine samples, urine without any preservatives can be stored at -22°C for over a decade without significant degradation. Measurement values after 12 years of storage did not differ from baseline values for more than half of analytes. Fifteen analytes exhibited high correlation between baseline and 12-year values, while the recovery rate of analytes with weak correlation did not drop under 70%.
- DNA and miRNA – A study of serum samples from the Janus Serumbank revealed that even after 40 years, serum samples stored at -25°C are viable for whole-genome sequencing and SNP calling, as well as qPCR and small RNA sequencing, with 650 unique miRNAs detected, on average, in each sample.
- Proteins – Stability of proteins in plasma varies from molecule to molecule; however, available evidence suggests that, when stored at -80°C for up to 6 years, proteins and other molecules in plasma samples do not degrade over time.
- Small molecules – Another study of the serum samples at Janus Serumbank revealed that sodium, calcium, iron, and creatinine levels do not significantly change over time if the serum is stored at -25°C. Serum levels of other analytes, however, may be substantially altered over time; the study revealed a 26.4% increase in potassium levels and a 59.4% decrease in bilirubin levels after storage for 25 years.
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