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More and more tests are emerging that will respond if people have antibodies to SARS-CoV-2. Many are rapid tests, which do not need to be sent to any laboratory. Fast, well-functioning tests could make a big difference in a situation where healthcare and the elderly want to increase the pace of testing. Furthermore, antibody tests could be a support in the diagnosis of suspected covid-19 despite the negative results of PCR assays, tests that are now standard.
But how good the tests are and how the results should be interpreted is uncertain. The Public Health Authority considers that an evaluation of rapid tests with CE marking is urgent, where they can be compared with validated laboratory tests. The authority has now summarized the state of knowledge, based on a basis developed by experts from the Karolinska Institute.
Laboratory antibody tests are often Elisa tests, a long-established test method. Rapid patient closure tests are of a different type and rapid tests are generally considered less accurate in the review. There is also a great variation between different speed tests in terms of quality.
Some tests measure the presence of IgM, antibodies that form fairly early during a viral infection and may be present when they are infectious. Expert judgment is that IgM-responsive antibody tests against sars-CoV-2 are of limited value and do not serve as the sole diagnostic method. It is unclear how high the risk of both false positive and false negative test responses is.
Hit safety when trying to explain to healthy people is also considered worse than for IgG antibody tests. At the same time, the review is recommended not to perform IgG testing prematurely in the course of the disease. So the risk of false negative responses is great. In several studies, only about half of the patients had developed an IgG antibody response within the first week of symptoms. It is also unclear if someone with mild symptoms even gets a measurable IgG response.
The Public Health Authority also notes that those who have IgG antibodies after SARS-CoV-2 are likely to have some protection against the disease in a new infection, even if it is unproven. How long the effect lasts in this case, how strong the protection is, and whether the degree of immunity varies between individuals is also unclear. In other words, according to the review, it is impossible to expect that you will be protected against a new disease because you have had covid-19, and especially not in the long term. Continuous research can clarify the picture.
Public health review: serology for covid-19
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