Exploring beyond the limit: How comparative stochastic performance affects retesting outcomes in six commercial SARS CoV-2 nucleic acid amplification tests

OBJECTIVES: To examine the comparative stochasticity profile of six commercial SARS-CoV-2 nucleic acid amplification tests (NAATs) and how this may affect retesting paradigms.

METHODS: Commercial quality control (QC) material was serially diluted in viral transport media to create a panel covering 10-10,000 copies/ml. The panel was tested across six commercial NAATs. A subset of high cycle threshold results was retested on a rapid PCR assay to simulate retesting protocols commonly used to discriminate false positives.

RESULTS: Performance beyond the LOD differed among assays, with three types of stochasticity profiles observed. The ability of the rapid PCR assay to reproduce a true weak positive specimen was restricted to its own stochastic performance at the corresponding viral concentration.

CONCLUSION: Stochastic performance of various NAATs overlap across low viral concentrations and affect retesting outcomes. Relying on retesting alone to discriminate false positives risk missing true positives even when a more sensitive assay is deployed for confirmatory testing.