Rapid tests for coronavirus
Comparison of reliability with PCR tests
Viktor Bobrovnikov, "Precedent TV"
The cost of one set of rapid tests for COVID-19 antigen and antibodies varies. For antibodies from 450 from 2000, and for antigen from 1500 to 4,500 rubles. The rapid antibody test kit includes: an alcohol napkin, a scarifier, instructions, a tablet on which the result will appear (a test cassette), to get the result, you need to take blood from your finger.
For the antigen test, you need to take a nasal mucosa sample and apply it to a test strip.
Evgeny Pechkovsky, Candidate of Biological Sciences, member of the Presidium of the Federation of Laboratory Medicine of Russia, consultant to the Director General of the Invitro Independent Laboratory, and Olga Verba, Doctor of Medical Sciences, Vice President of the Association of Aviation Medicine Doctors, answered the questions of the "Precedent" about express tests.
– How reliable are such rapid pharmacy tests?
– The condition for the accreditation of the laboratory by Rospotrebnadzor is the confirmation of more than 85% of the results by the second independent test in the RPN. Each rapid test is characterized by its own detection threshold (sensitivity). The sensitivity threshold is the limit below which the test does not determine the presence of coronavirus antigens or antibodies to it. The sensitivity of the rapid antigen test is two orders of magnitude lower than that of a conventional PCR test performed on a good manufacturer's test system.
That is, the probability of skipping the initial stages and getting a false negative result is 100 times higher than in the case of PCR analysis in an accredited laboratory. I specifically focus on this, since there are a lot of fake performers of analyses. If you want to get a real result, then all accredited laboratories for performing tests on Covid–19 are on the RPN website, - says Evgeny Pechkovsky, – In addition, doing the analysis yourself, you risk making a mistake, for example, when taking a smear and if you read the native instructions in English, then it is written in black and white "not for personal use", but people bought a bunch of such systems and they need to sell them, and with such a comment, pharmacies did not take these tests for implementation. So apparently I had to pay so that this line in the instructions disappeared and a vague wording appeared about the possibility of using unskilled personnel.
– What is an antigen and antibodies?
– An antigen is fragments of proteins foreign to the body and/or polysaccharide in this case of our coronavirus. The rapid test strip contains antibodies to these antigens. Antibodies to SARSCoV2 are only marker molecules that mark the cells of the body affected by a specific virus, after which they are recognized by the cells of the immune system and proceed to destruction. The body does not know how to treat cells. He's killing them. The number of antibodies is important, but the presence of immunocompetent killer cells is more important. Their qualification is the characteristic of T-cell immunity, which allows us to conclude that your body is protected," says Yevgeny Pechkovsky.
– Viral antigens are proteins and/or polysaccharides that are part of the virus, which are recognized by the immune system. Analysis for viral antigens is another test for the diagnosis of coronavirus infection, including in those who have been in contact with it. The absence of viral antigens also means that a person has no infection. But, as in all other tests, the result is relevant only at the time of the analysis and does not guarantee that a person could not get infected later, after the study," adds Olga Verba.
– How long can antigens and antibodies stay in the body?
– IgM and IgG are immune cells that are produced in the human body as a result of its contact with the virus. IgMs are produced at the very beginning of the disease, they usually appear 3-5 days after the appearance of the first symptoms and indicate an ongoing acute disease – the current infection. IgG appear when a person has overcome an infection, usually 10-14 days after the onset of the disease and remain long enough after the disease. It is generally believed that their presence indicates a transferred disease and emerging immunity. It is still unknown how long IgG antibodies will remain in the blood and protect against re–infection," Olga Verba said.
– What legal force do the results of the pharmacy express test have?
– Such a result cannot have official force, since no one can record that it was you who passed this test, maybe you took it from your child or dog. Right in the text of the instructions for the express test, it is recommended to retake alternative laboratory methods in case of a positive result. That is, again, PCR. Pay 2 times. Now the load in accredited laboratories has subsided, decreased by about the same 2 times and it is quite possible to make an analysis within a day or two in Novosibirsk. Express tests are still a screening for complacency, which may end and just rest," Pechkovsky summed up.
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