As Poslovni Dnevnik writes on the 29th of October, 2020, given the news of long queues which have become somewhat synonymous with coronavirus tests, it has become more and more desirable to have some alternative to standard laboratory PCR tests. About a month ago, news surfaced about the availability of antigen tests. Such coronavirus tests are fast, the result is obtained in half an hour, it isn’t too expensive, with a price of 250 kuna, and they’re offered by different manufacturers, according to Vecernji list.
”Yes, they’re definitely be recommended. But they must be antigenic, not serological. Although they have a slightly lower sensitivity than PCR tests, they can be done outside of a laboratory, for example in a nursing home, school, anywhere, they’re cheaper so many more people can be tested,” said prof. dr. sc. Branko Kolaric, an epidemiologist and member of the Scientific Council of the Croatian Government. The usefulness of such coronavirus tests has been confirmed by well known Croatian molecular biologist prof. dr. sc. Nenad Ban at ETH in Zurich, Switzerland.
”The test can be used to detect the presence of a viral protein that surrounds the SARS-CoV-2 genome when in our body. It’s relatively fast and specific, so it won’t detect proteins that exist in other related viruses. Given the sensitivity claims of about 95 percent, it means that it is possible that every twentieth test doesn’t detect the presence of the protein despite its existence. This test is significantly different from previous coronavirus tests that detected the presence of antibodies to the virus because antibodies begin to develop much later than when a person becomes ill, so, the antibody test couldn’t be used to determine if someone is contagious or not,” explained the scientist.
Viruses are very small, SARS-CoV-2 is about 100 nm, and consequently they have very little antigen, as was learned from doc. Dr. Vanda Juranic-Lisnic from the Faculty of Medicine in Rijeka.
”There must be enough of the virus to be visible to the antigen test, and usually when a patient has a lot of virus, he has symptoms. Unlike tbe PCR test, previous antigen tests have much lower sensitivity. Clearly, given the efforts of the scientific and medical community, we’re sure to get increasingly sensitive antigen tests. Based on past experiences, it may be found that antigen tests are well applied in the rapid testing of symptomatic patients to quickly determine whether they’ve contracted COVID-19 or some other type of respiratory infection. However, it should be borne in mind that the negative result of the antigen test must be additionally confirmed by a PCR test precisely because they’re less sensitive,” stated Dr. Juranic-Lisnic.
Prof. dr. sc. Zlatko Trobonjaca from the Medical Faculty in Rijeka explained how such a test works.
”These tests are based on the colour change of the reactants in the presence of an antigen that is recognised and captured by specific antibodies. This antigen in the detection of the SARS-CoV-2 virus is a nucleocapsid protein, so its presence and detection also indicates the infection of the subject. The problem with these tests is the fact that the antigen concentration may be too low to detect and therefore they’re recommended only in the stages of the disease in which we expect higher levels of the virus on swabs and thus higher amounts of antigen. And that means in the first few days of the disease (up to 7 days), in cases with too little concentration of antigen, we can expect false negative findings,” said Dr. Trobonjaca.
The American experience is certainly the most extensive, so prof. dr. sc. Maria Skugor of the Cleveland Clinic was asked about these types of coronavirus tests.
”They’re very fast and easier to use, but they’re not that sensitive yet and a negative result doesn’t actually exclude infection. The specificity is about 98 percent, but the sensitivity is, in my conservative estimate, about 60 percent. Therefore, symptomatic patients with a negative test should have an RT-PCR test,” said Dr. Skugor.
”There’s a noticeable difference in experiences when it comes to sensitivity, and the possible reason is the manufacturer. The quality of these tests depends on the quality of the manufacturer and therefore you should test the quality before buying large quantities of tests,” said prof. dr. sc. Ivan Djikic from Goethe University in Frankfurt.
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