Researchers from the US demonstrated that rapid antigen (RAT) tests for SARS-CoV-2 are more effective in determining the actual infection status of COVID-19 positive patients. The RAT has recently been approved by the FDA and is a type of immunoassay that directly detects the presence of a viral protein.
The scientists performed both antigen-based and PCR-based tests using respiratory swabs. The results were then compared with the SARS-CoV-2 TMPRSS2 culture of the swabs. This viral culture is a sensitive culture test for determining the virus and is used as the reference method for determining infectiousness. Of the 38-PCR-derived positive samples, 28 were positive while 10 samples were negative in virus culture testing. All but one sample was positive in an antigen-based test. Amongst the 10 samples that were positive in PCR but negative in viral culture, two were positive in the antigen-based testing. With a study prevalence of 11%, which was determined by virus culture-positive results (a total of 251 samples), the PCR test and antigen test showed positive predictive values of 73% and 90%, respectively.
The study concluded that antigen-based test results correlate better with viral culture results. The antigen tests revealed 96% sensitivity and 98% specificity, whereas the PCR test showed 100% sensitivity but 95% specificity. The RATs perform better in presence of infections and it is possible to detect viral RNA in swab samples by the PCR tests even after the complete attenuation of the infectious virus.
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