Impact of storage temperature and duration on rRT-PCR Cycle Threshold (Ct) values in SARS-CoV-2-positive nasopharyngeal Samples: A study at a provincial hospital in Morocco

Résumé fourni par la source

Reverse transcription polymerase chain reaction (RT-PCR) is the gold standard for SARS-CoV-2 diagnosis of infection. Pre-analytical factors such as storage temperature and duration may affect RNA stability and, consequently, RT-PCR performance. This study aimed to assess the impact of these factors on cycle threshold (Ct) values to ensure reliable diagnostic results. Eighteen SARS-CoV-2–positive nasopharyngeal swab samples were stored at +4 °C and −20 °C and analyzed by RT-PCR over a period of 1 to 7 days. Detection of the S (Spike) and RdRp (RNA-dependent RNA polymerase) genes was performed, and Ct values were compared before and after storage. All analyses were conducted using the same standardized protocol for RNA extraction, amplification, and result interpretation. All initially positive samples remained positive after storage. Ct values showed only minor variations, with mean decreases of −1.02 cycles for RdRp and −1.05 cycles for the S gene after storage. Variations of up to 2–3 Ct cycles were observed in some samples. These findings suggest that short-term storage under standard conditions is unlikely to affect SARS-CoV-2 detection by RT-PCR. Because of the limited sample size, the analysis was mainly descriptive. Therefore, short-term storage of SARS-CoV-2 samples under routine laboratory conditions did not alter RT-PCR qualitative results.

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