• Nahal Eshghifar, Ali Busheri, Rojeet Shrestha, and Safedin Beqaj.
• UltimateDx Laboratories, Los Angeles, CA, USA.
• Int J Gen Med. 2021 Jan 1; 14: 435-440.

BackgroundEarly diagnosis of the novel coronavirus disease of 2019 (COVID-19) in asymptomatic and symptomatic patients is crucial to identify infectious individuals and to help prevent the spread of the virus in the community. Several assays have been developed and are in use in today's clinical practice. These assays vary in their analytical and clinical performance. For an accurate diagnosis, medical professionals must become more familiar with the test's utility to select the most appropriate test. This study aims to evaluate the analytical performance of rapid antigen tests used for the detection of SARS-CoV-2 viral antigen compared to RT-PCR SARS-CoV-2 molecular assay.MethodsOropharyngeal swab specimens from five COVID-19 patients were tested by seven rapid antigen tests developed by different IVD companies. RT-PCR to detect specific RNA fragments of SARS-CoV-2 was used as a confirmatory test. The cycle threshold (Ct) value, which often reflects viral load, in these specimens ranged from 15 to 35. For the analytical evaluation, extraction fluid of each antigen kit was spiked with attenuated ATCC virus at different concentrations ranging from 4.6x104/mL to 7.5x105/mL and tested with antigen testing kits.ResultsOut of five confirmed positive SARS-CoV-2 specimens by RT-PCR, only one sample showed a positive result by one of the seven evaluated antigen testing kits. The positive result was observed in the specimen with a Ct value of 15. All other evaluated rapid tests were negative for all five positive specimens. This was further confirmed with the spiking study using ATCC attenuated virus, where extraction fluid of each rapid test was spiked with concentrations ranging from 4.6x104/mL to 7.5x105/mL. None of these spiked specimens showed positive results, indicating very low sensitivity of these antigen kits.ConclusionThis comparison study shows that rapid antigen tests are less sensitive than RT-PCR tests and are not reliable tests for testing asymptomatic patients, who often carry low viral load. Analytical performance of rapid antigen tests should be thoroughly evaluated before implementing it at clinical decision level.© 2021 Eshghifar et al.

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