May 11, 2020
Many people who have recently had illnesses whose symptoms match Covid 19 disease are asking themselves whether it could have been the new virus.
Antibody laboratory tests could provide information about this. Great progress has been made here in the recent past – with the prospect of wider use, experts in the APA interview.
☣️➡️ More on this topic ⬅️☣️
While the currently widely used PCR tests directly detect the genome of the SARS-CoV-2 virus, antibody tests – including both rapid tests, e.g. so-called ELISA laboratory tests and neutralization tests – have another target object: They look for the traces that the Has grappled with the novel corona virus in the body’s defense system.
In order for the immune system to defend itself against the pathogen, it must recognize it as an attacker. Antibodies are produced that specialize in detecting and rendering the virus harmless – and this is what these test procedures, which require blood samples, are searched for.
The problem with coronaviruses is their diversity and the fact that they can also usually trigger mild diseases in humans. Especially infections with such low pathogenic human Coironaviruses, which already existed in our latitudes before Covid-19, occur relatively frequently.
If the body has developed antibodies against these relatives of SARS-CoV-2, this can lead to a test for the currently rampant virus being false positive.
Rapid tests are not always reliable
This risk is particularly great in the case of rapid tests which are intended to indicate an infection more or less immediately and without equipment and specialist knowledge. With such methods, a few drops of blood are supposed to suffice for the detection.
Although these tests were on the market very early on, “most of them did not achieve what conventional laboratory tests achieve both in terms of sensitivity and specificity,” said Gregor Hörmann of the Austrian Society for Laboratory Medicine and Clinical Chemistry (ÖGLMKC) the APA.
Hörmann therefore names two key terms for the quality of analyzes: sensitivity denotes the detection limit of a method. The term therefore describes the lowest concentration of the material sought that can be found with the test. High analytical sensitivity indicates that there is a high probability that the test will work if there are antibodies.
The analytical specificity, on the other hand, shows the ability of the test to respond precisely to the substance sought and not to similar compounds. High specificity avoids false positive results – that is, an infection that has not occurred is displayed.
In both areas, tests of rapid tests by Ursula Wiedermann-Schmidt and her team from the Institute for Specific Prophylaxis and Tropical Medicine at the Medical University of Vienna showed great weaknesses.
At the beginning of the pandemic, there was a lot of hype surrounding these procedures and the market was also flooded with products that were not validated at all, according to the scientist, who tested several rapid tests that were submitted to the German government. “The yield in terms of sensitivity and specificity was not very good,” said the researchers, who also did not recommend this test group for the dark figure studies.
In the laboratory-dependent tests, however, “we are currently in a phase of change,” said Hörmann. So far, many processes have led to false positive results of one to two percent, which is unsatisfactory and in many cases necessitates counterchecks by means of a so-called neutralization test.