Negative Results of Nucleic Acid Amplification Tests for SARS-CoV-2 in Clinical Practice May Vary among Six Molecular Assays in Patients with COVID-19.

Several commercial nucleic acid amplification tests (NAATs) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been developed. We used 6 kits available in Japan in 13 NAAT-positive specimens with crossing point values >36 and 7 NAAT-negative specimens from patients with coronavirus disease 2019 (COVID-19), and their results were compared. Specimens positive in ≥2 assays were considered true-positive and examined for concordance with the specimen results. The SARS-CoV-2 Detection Kit -Multi- (Toyobo M; Toyobo, Osaka, Japan) using extracted RNA had the highest concordance (κ = 1.00). This was followed by Cobas® SARS-CoV-2 (Roche, Basel, Switzerland) (κ = 0.79). There was a weak correlation between the number of negative results for each kit and the number of days between onset and testing (Spearman rank correlation: ρ = 0.44; P < 0.05). We believe that the variations in results among kits for specimens with low viral loads should not be problematic when these kits are used for screening infectious patients because these variations are more likely to be observed in specimens tested many days after onset (i.e., those that have lost their infectivity). However, it may be better to use a test for suspected late-stage COVID-19 with a low viral load, such as Toyobo M or Cobas.