Diagnostic Accuracy of SARS-CoV-2 Nucleocapsid Antigen Self-Test in Comparison to Reverse Transcriptase-Polymerase Chain Reaction

Abstract

Background: Currently, the rapid antigen test (RAT) and reverse transcriptase-polymerase chain reaction (RT-PCR) are considered the main stakeholders in COVID-19 diagnosis. In RT-PCR, any of at least 2 evolutionary conserved genes (RdRP, E-, N-, ORF1ab gene) and S-gene of SARS-CoV-2 are endorsed, and in RAT, the nucleocapsid antigen (N-Ag) of SARS-CoV-2 is considered due to its stability and fewer chances of mutation effects. In the present work, we evaluated the performance of the AG-Q COVID-19 N-Ag self-test kit and conducted a validation study in comparison with the RT-PCR.

Methods: AG-Q COVID-19 N-Ag rapid test kit is an Indian Council of Medical Research (ICMR) approved product developed and marketed by Agappe Diagnostics Limited. The RT-PCR assay was performed with a COVIPATH COVID-19 RT-PCR kit from Thermo Fisher Scientific.

Results: We observed 19 false-negative results in antigen self-tests, including samples of threshold cycle (Ct) values 22/22 (N-gene/ORF1ab-gene) in RT-PCR, indicating inadequate sampling by the patients in self-tests, leading to false-negative results and increased chances of the disease spreading. Based on the RT-PCR Ct value vs antigen self-test comparison, it is evident that proper sampling is crucial in performing antigen self-tests. Also, there were weak positive results in antigen self-tests with a Ct value of 18/19 in RT-PCR.

Conclusions: Although the sensitivity and diagnostic accuracy offered by the AG-Q COVID-19 N-Antigen self-test in comparison with RT-PCR fulfills the ICMR tenets for RAT, this study recommends the laboratory/hospital-based RAT execution would be appropriate, rather than the self-test.

Keywords: COVID-19; N-antigen; RT–PCR; colloidal gold; self-test.