The scientist has discovered the truth about the tests for coronavirus: why there are mistakes

– Denis Vladimirovich, align please our readers in the diversity of available diagnostic tests.

– the Most common test to identify the virus genome. Some viruses (HIV, influenza, coronavirus) genome is represented not by the DNA molecule, and RNA — RNA. But the essence of the test remains the same, it is a common DNA-diagnostics. In the vast majority of cases it is based on the method of PCR — polymerase chain reaction. It is the most reliable method of DNA diagnostics, the gold standard determination of viral infections. On average, the study takes 3-4 hours. But since we have to deliver a sample to the lab, register it, etc, then go a little more. Usually lab say that doing the test from 8 hours to 2-3 days. If some laboratories claim that “the Result will be today”, and others say it’s only 3 days, this is not due to duration of the actual analysis, and logistics processing of biomaterial.

– Who produces these tests?

– At the beginning of April in Russia for seven manufacturers of test systems for DNA diagnostics have a registration certificate of Roszdravnadzor (the document authorizing the test in clinical laboratory diagnosis). More or less they are all the same in their sensitivity and specificity. Although the first test recommended for use in February, differed slightly lower sensitivity.

– That is, in the case where one analogue gave a positive result indicating the disease, the other could give negative?

– Yes, different test systems may give different answers because of different according to the manufacturer the sensitivity of the reagents. In addition, there is the factor of “doctor”: in one case the patient could take more of the virus and his system, “saw”, in the other — the tube got less viral particles, and the response was a false negative.

When we say prepared so much EDINIC test systems, what do you mean?

– One test is a combination of reagents designed for analysis of one sample of biological material (one patient). It involves several steps. The first stage is the release nucleic acids from the virus (takes 30-40 minutes), then comes the stage of reverse transcription — the conversion of RNA to DNA and PCR amplification (1,5 hour).

Each set of reagents, typically supplied in the kit for the analysis of 96 samples. Therefore, the figures supplied test systems sometimes swim: someone said sets, some with unit tests. More correct to count in units.

More recently seems to be a shortage of such PCR tests. And today, we are told that Russia is supplying test systems in 30 countries. We do enough tests all over the country?

Seven producers cope with production. Historically, we have good capacity for the production of such reagents.

Why people sometimes long wait for results? My colleague with suspected infection of SARS-CoV-2, waiting for the results of the analysis for more than a week.

– the fact that two weeks ago the results were required to confirm at the Novosibirsk center “Vector”. If in Moscow we found a positive sample had a test copy to deliver to Novosibirsk. While the tests were delivered there, then back, passed just a few days. Today, the sending of the second sample analysis of clinic is to re-confirm not in Novosibirsk and in the Moscow regional centre. It takes 1.5-2 days.

– the same system operates in other regions of Russia?

– Yes.

When you take a swab, the patient reported that for the test who is the manufacturer?

– If this is not a commercial study, then probably not. But I can assure you, today all tests are classified as highly sensitive.

– And yet, if the person passed the biomaterial on the first analysis, and it gave a negative result when he prescribed the re-sampling?

three days later, when in a biological sample of the virus particles will be more. During these three days the person should be isolated. If the two times test will give a negative result, in this case, the diagnosis COVID-19 not assigned.

Re-analysis is also performed in two laboratories?

Yes, the rules require independent confirmation in a reference laboratory.

– And how likely is the variant with a false-positive result? After he did not re-nominate analysis?

– the Probability of a false-positive response in two repeated tests in different laboratories is less than 0.01%, that is actually missing.

Wednesday, Rospotrebnadzor announced that the number of laboratories starting in Moscow mass screening everyone through paid highly sensitive test system. That is, any city resident may request the diagnosis and his house will bring everything you need.

– as far As I understand, we are talking about the same commercial laboratory practiced before – provided similar services with the collection of bioprobe at home.

even Offer an option that would allow the patient to take bioprobe and send to the lab…

the Initiative in this case may give an incorrect result. To take a swab from the throat needs a doctor or a trained technician. If a patient does not gets in there, it could be a false-negative response.

Why a swab taken from the nose and throat?

– So at the moment the algorithm of taking the biomaterial, although, in fact, more accurate is a swab from the throat.

blood to identify the disease?

– For the way PCR can be used as a smear, and blood.

Now increasingly promoting a rapid test for the detection of viral particles in the form of thoseSt-strips. It is an alternative to PCR?

– Most likely, when it comes to test strips, refers to the ELISA immuno-enzymatic analysis. Analysis of viral particles can be produced by using ELISA, but it is unlikely it will be today to use. The fact that the accuracy and sensitivity it is inferior to the method described above PCR. But there are already similar test strips for ELISA test for the presence of antibodies in the blood, already ill COVID-19. Here they are very effective and give results in a few minutes.

So be careful when ordering, rapid tests, carefully study their purpose. By the way, some manufacturers of test systems for PCR diagnostics can and its called the rapid test, in principle, 3-4 hours, during which it is performed, is not a term.

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