Clinical comparison of three SARS-CoV-2 nucleic acid amplification tests for routine diagnostic testing

Cycle threshold (Ct) values from SARS-CoV-2 nucleic acid amplification tests have been used to estimate viral load for treatment decisions. Additionally, there is a need for high-throughput testing, consolidating a variety of assays on one random-access analyzer.

In this study, the clinical performance of the Alinity m SARS-CoV-2, RealTime SARS-CoV-2, and GeneXpert Xpress SARS-CoV-2/Flu/RSV assays was assessed.

Alinity precision and detection rates were evaluated using a dilution series of the Alinity m SARS-CoV-2 positive control. In a retrospective study, 7 remnant external quality assessment (EQA) specimens and 200 remnant nasopharyngeal swab specimens (100 positive and 100 negative) were tested in the three assays.

Alinity had 100 % detection rate at 50 copies/mL and high reproducibility (Ct value coefficient of variation ≤3.1 %). All three assays correctly detected positive and negative EQA samples with comparable Ct values (max difference 2.38) and high linearity. In patient samples, positive percent agreement was 95 % (95 % CI 89-98 %) and negative percent agreement was 100 % (95 % CI 96-100 %) for Alinity, compared to the other two assays. Four specimens detected on Alinity m but not RealTime or Xpert had Ct values above 40. Assay results were highly correlated (r ≥ 0.94). Ct values (after addition of 10 unread cycles to the reported Ct of RealTime) were comparable across the three assays.

Alinity m had high precision and accuracy and Ct values comparable to those of the RealTime and Xpert assays. The assays could be used interchangeably, with no need for adjustment of patient management decisions based on Ct values from each assay.