Understanding Rapid Antigen Testing for COVID-19

Antigen tests detect a PIECE of the SARS-CoV-2 virus and may have a role in diagnosing COVID-19 in those with active COVID infection. However, since it does NOT have an amplification step like PCR, it is less sensitive and is best used in people with relatively high levels of viral replication which occurs mostly in people who are either about to or already have symptoms.

Rapid Antigen Test vs. RT-PCR Testing

Rapid Antigen Test vs. Rapid Antibody Tests

POSSIBLE USES OF RAPID ANTIGEN TESTING:

1. As a screening test for LOW RISK individuals. At a pretest probability of 5% or less, an RT PCR (sensitivity 62% specificity 100%) will result in a 98% negative predictive value. For antigen test, (positive percentage agreement with RT-PCR 80% = 50% sensitivity, specificity 100%) will have a negative predictive value of 97%. For this purpose, a properly validated antigen testing may be an acceptable and quick substitute for screening low risk patients like those for elective procedures, or for those about to travel or enter tourism bubbles.
2. As an initial test for symptomatic patients. Since the sensitivity is only about 50%, this should NOT be used as a standalone test and should be supplemented by RT PCR if it is negative. But if it is positive, then you would have identified a positive case within one hour (versus 2 to 3 days for RT-PCR) and isolated and contact traced much faster.
3. As with all tests, antigen tests are not perfect and should only be used under the supervision of a licensed healthcare professional. It should be properly validated and we should only use kits with at least an 80% positive percentage agreement with RT-PCR. Biosafety protocols for PPE and processing need to be strictly followed to prevent inadvertent infection. As we try to turn the tide of COVID-19 in our country, we need all the tools we can muster in this fight. Used properly, antigen testing can speed up case identification and contact tracing in unprecedented ways.

Reference:
Edsel Maurice Salvana. (2020, August 03). Understanding antigen testing for COVID-19 [Facebook update]. Retrieved from https://www.facebook.com/1699193450/posts/10207918904366025/