In the midst of the Omicron variant of the coronavirus, thousands of tests are performed daily in the country, which is trying to shield itself against this “wave”. Some of the tests are done with rapid tests or self tests, while others are performed in laboratories with molecular tests, the so-called PCR. As the latter is the most reliable method of detecting coronavirus, many people rush for a PCR test when they suspect they are ill or when they have a positive self or rapid test to confirm the result.
However, there are cases in which the rapid or self test comes out negative, and even many times or for several days, and then the PCR is positive. To answer why this is happening, Assistant Professor of Epidemiology and member of the Committee of Experts, Gikas Majorkinis, proceeded to a post on social media, in which he presents a fact to explain exactly why this discrepancy of results occurs.
Professor Gika Mayorkin’s post:
Here is an anonymous fact that shows why PCR should be used sparingly and interpreted by qualified personnel in conjunction with the rapid antigen test.
A colleague asks my opinion about an incident where he has symptoms of respiratory and fever, while the rapid antigen test is negative for 2 days. Due to persistence of symptoms (day 3) a molecular SARS-CoV-2 test was requested which came out positive in high cycles (low load). On the 4th day, the rapid antigen test is repeated, which is still negative.
At that time, a syndromic panel was requested, which revealed the real culprit of the fever (parainfluenza virus). The (vaccinated) patient had passed SARS-CoV-2 asymptomatically within the last month and was infected with another virus with similar symptoms and was found to be positive for SARS-CoV-2 PCR.
Conclusions:
1) Positive PCR at low loads with negative antigen probably means old (> 10 days) undiagnosed SARS-CoV-2 infection
2) as the duration of positive PCR-negative antigen is much longer in the escape of the infection (average 17 days, it reaches up to 83 !!! days), the first thing to think about is old infection, despite the onset of infection
3) if the antigen is negative and the PCR is positive, always look at the load (PCR cycles), at low load ask for a repeat of the PCR or a repeat of the antigen after 1 day. If the antigen does not become positive in the next 1-2 days or the load remains low, we should consider alternative diagnoses.
4) I recommend the execution of the syndromic panel in severe cases with prolonged discrepancy between PCR and rapid antigen of SARS-CoV-2
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