Study Evaluates Molecular Diagnostics Tests for SARS-CoV-2

The explosion of COVID-19 cases in the USA has highlighted the critical role diagnostic testing plays in medical and public health decision making in containing and mitigating the SARS-CoV-2 pandemic.

Reverse transcription polymerase chain reaction (RT-PCR) is the mainstay of SARS-CoV-2 detection in vitro. The authorized assays for SARS-CoV-2 have mostly targeted two loci of the coronavirus. Conducting head-to-head evaluations of technologies is one of the best ways to know how well tests work. In a crisis, though, these evaluations must sometimes take a back seat to patient care. Almost four months into the COVID-19 outbreak, test comparisons are now popping up at a rapid pace and positive sense, single-stranded RNA virus by real time RT-PCR and are reported qualitatively.


Medical Laboratory Scientists at the University of Washington Medical Center (Seattle, WA, USA) collected 169 nasopharyngeal (NP) swabs from patient specimens submitted to the University of Washington Medical Center laboratories for clinical diagnostic testing. The team compared the analytical performance of a laboratory developed test (LDT) developed in their clinical laboratory based on CDC primer sets and four commercially available, FDA emergency use authorized assays for SARS-CoV-2. These were: the Xpert Xpress SARS-CoV-2, (Cepheid, Sunnyvale, CA, USA); the Simplexa COVID-19 Direct Kit (DiaSorin Molecular, Cypress, CA, USA); the Panther Fusion SARS-CoV-2 test (Hologic, Bedford, MA, USA); and the cobas SARS-CoV-2 Test (Roche Diagnostics, Risch-Rotkreuz, Switzerland).

The scientists reported that the LDT and Cepheid Xpert Xpress SARS-CoV-2 assays were the most sensitive assays for SARS-CoV-2 with 100% agreement across specimens. The Hologic Panther Fusion, DiaSorin Simplexa, and Roche Cobas 6800 only failed to detect positive specimens near the limit of detection of the CDC-based LDT assay. The in-house LDT demonstrated 100% concordance with the Cepheid Xpert Xpress, also detecting the extremely low viral load specimen as an inconclusive.

The authors concluded that all the assays were 100% specific, using the CDC-based LDT as the gold standard. The results provided initial test performance characteristics for SARS-CoV-2 RT-PCR and highlight the importance of having multiple viral detection testing platforms available in a public health emergency. The study was published on April 29, 2020 in the Journal of Clinical Microbiology.