An international team of scientists conducted a study, during which they decided to find out why tests for coronavirus give false positive results in almost 20% of cases and whether such tests have an alternative.
Today, polymerase chain reaction (PCR) tests are the standard diagnostic tool. viral respiratory infections. This is a molecular test that detects viral genetic material indicating the presence of an actual virus, such as SARS-CoV-2, which causes COVID-19.
PCR tests remain the standard diagnostic test primarily for those with symptoms of the virus. The tests are very sensitive and can detect small amounts of viral genetic material (RNA) in a sample.
Samples can be taken either as a throat swab through the mouth (oropharynx) or through the nose (nasopharynx). During the coronavirus pandemic, special reagents and equipment needed to conduct PCR testing for COVID-19 were in short supply.
Another problem is that PCR tests for COVID-19 are flawed due to the fact that the virus is still new. It can also take from 10 to 24 hours to decrypt and analyze the material.
PCR tests require specialized equipment and highly qualified personnel. And importantly, they are primarily intended for diagnosis in people with symptoms. They showed low efficiency in people with an asymptomatic form of the disease. As we know, in the situation with the coronavirus, asymptomatic patients are one of the most dangerous carriers of the disease. — they write scientists.
The tests can give false negative results in people who are actually infected. This happens in 20% of COVID-19 PCR tests. The factors influencing the results are the timing of sampling, for example, the analysis is taken soon after infection or too late, when there are practically no viral particles.
Are there any alternatives?
Tests that detect antibodies to SARS-CoV-2 can be used to complement laboratory research and fill in the gaps due to the nature of COVID-19 PCR tests. As a reminder, PCR tests detect the actual virus in the smear, while antibody tests detect the human immune response on the virus.
Antibody tests have been successfully implemented in USA, Great Britain, France and Germany as useful laboratory tools for additions COVID-19 PCR tests. The appearance of antibodies in viral infections usually follows the same pattern.
But even antibody tests are not a panacea, scientists write.
Research showthat the period of effectiveness of this test is 10-14 days from the onset of the symptom to the detection of antibodies. This means that antibodies can only be detected with antibody tests about two weeks after infection.
It is also still unknown whether the IgG antibodies detected by antibody tests indicate immunity to the virus and how long such protection may last.
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