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Until recently, the only criterion for diagnosing COVID-19 was a positive result of a molecular PCR analysis. Rapid antigen testing is currently an equivalent method for confirming infection in patients with symptoms. What stands out express test for coronavirus? Is it as effective as PCR analysis?
Antigen tests - what is this?
Antigen tests allow detecting protein particles — antigens of the SARS-CoV-2 virus. For this, the immunochromatographic method is used. The selected sample is applied to the hole in the test plate. After the corresponding time has elapsed, the result is read.
An undoubted advantage of express tests for antigens is the simplicity and speed of execution, which also leads to lower costs. The biggest drawback is lower sensitivity than RT-PCR. However, many experts believe that this is sufficient for diagnosing COVID-19 and is necessary in the current epidemiological situation. WHO recommends using express tests for antigens in the absence of the PCR method or a long wait for the result.
According to WHO recommendations, antigen tests should have a sensitivity of 80% and a specificity of 97%. Due to the risk of obtaining false-negative results, experts recommend using tests with diagnostic sensitivity of 90% and specificity of 97%.
Testing for antigens - how to collect a sample?
A sample for analysis is taken from the nasopharynx, similar to genetic testing using PCR. Taking a smear may cause slight discomfort, but it is quick and completely safe.
Antigen tests - when is it carried out?
Due to the lower sensitivity of the method in relation to PCR, the period during which it is possible to detect the coronavirus is much shorter than in the case of a molecular test. The test should be carried out within the first 5-7 days after the onset of symptoms. Tests for antigens can be positive 1–3 days before the appearance of symptoms, since the amount of virus in the respiratory tract is maximal.
Antigen tests - where to test?
Antigen tests are intended for rapid diagnosis of patients with certain symptoms. They are used in hospital wards and emergency departments, as well as in ambulances.
The test can also be carried out at special points for analysis.
Antigen tests - how to interpret the results?
Antigen tests and PCR are considered equivalent methods of detecting COVID-19.
Currently, only people with symptoms typical of COVID-19 are tested. Due to the complex epidemic situation, infection can be confirmed only on the basis of a positive antigen test. A negative antigen test result in a patient with typical symptoms should be confirmed by PCR analysis, as this does not rule out infection. In conclusion, people with positive symptoms should be considered infected, and people with negative symptoms should be confirmed by molecular testing.
Antigen testing is mainly recommended for screening patients with symptoms of infection in areas with a high risk of infection and where rapid confirmation of infection is required. Antigen tests, despite their lower sensitivity, can significantly reduce the spread of SARS-CoV-2 infection.
