In Russia, an increase in the incidence of COVID-19 is again recorded. The experience of the pandemic has shown that timely testing helps to restrain the spread of infection. However, the existing rapid tests have serious drawbacks, and the crucial one is a fairly large percentage of false results. We sort out the common flaws of test systems and find out whether manufacturers manage to eliminate them
SARS-COV-2 antigen detection tests
Antigen tests detect the virus protein in the human blood. Among their advantages, we can note the high speed of obtaining the result (5-15 minutes) and ease of use. The major disadvantages are the unproven accuracy of the results in newly infected people and, as a rule, lower sensitivity compared to PCR tests (approximately 85-97.6%). Since 2021, the results of the antigen test have been equated at the legislative level with the results of the PCR test.
One of the most popular rapid antigen tests is BIOCREDIT Covid-19 Ag manufactured in South Korea. It is used to determine the antigen in people with clinical symptoms of respiratory disease and suspected COVID-19 infection.
The sensitivity of BIOCREDIT Covid-19 is in no way inferior to the analyses performed using the PCR method. Clinical and laboratory tests revealed: the sensitivity of the test is 96%, and the diagnostic specificity is 100%.
The principle of operation is as simple as possible: after taking a swab a biological sample should be placed in a test system, on the membrane strip of which antibodies specific to the coronavirus antigen have already been applied. If there is a virus on the T line, a black stripe will appear. The time to get the results is 5-8 minutes.
The SGTI-flex Covid 19 Ag test is also distinguished by its high accuracy and ease of use. Sensitivity to the virus protein is 96%, diagnostic specificity is 100%. False results when using SGTI-flex Covid 19 Ag are extremely rare.
Another Korean test that is widely used in the pharmaceutical market is Nowcheck Covid-19 Ag. Compared to the previous variants, it has a slightly lower sensitivity (89%) and specificity (97%). The principle of operation is similar, the time to get the result is from 15 minutes.
Tests for IgM and IgG antibodies to coronavirus
Antibody tests are aimed at detecting immunoglobulins in the body that fight the virus. This method helps to establish whether a person has had contact with a sick person, and more accurately identify hidden carriers of infection and those who have had Covid-19.
One of the most high-quality rapid tests is CAREUS Covid-19 IgM/IgG by a Korean manufacturer: it detects two types of antibodies at once and helps in confirming the diagnosis, as well as detecting those who have been ill. In addition, it is easy to use. If antibodies to SARS-Cov-2 are present, after adding blood drops to the test system, they will bind to gold nanoparticles — purple stripes will appear on the test. The sensitivity of the test is 93.6%, the diagnostic specificity is 98%. The time to get the result is 10 minutes.
The Korean Rapid Bio Covid-19 IgM/IgG test is also of high quality. Its accuracy is higher than that of the previous system — 96%. The specificity is 99%. However, waiting for the result may take a little longer — from 10 to 20 minutes. In addition, the analysis will require more biological material — 20 ml of blood (in the first case — 10 ml).
Another Korean test, SGTi-flex Covid-19 IgM / IgG, is inferior in terms of indicators to the two mentioned competitors: its sensitivity reaches 94%, specificity — 97%. At the same time, it is also simple and easy to use.
RBD tests can detect antibodies to the S-protein of the coronavirus - especially to its receptor-binding domain( RBD), which directly indicates immunity to infection. Such tests are used before vaccination to check the presence or absence of antibodies and thereby make sure that vaccination is necessary.
RBD tests also allow us to reliably detect antibodies after vaccination. Unlike most other rapid antibody tests on the market, which are designed to detect antibodies to alive virus, this diagnostic method is suitable for working with post-vaccination antibodies. Even where the antibody test of the previous generation would indicate the absence of immunoglobulins, the new system gives the correct result.
Among the RBD tests, the Korean SGTI-flex-19 IgG is considered to be one of the most reliable. The sensitivity and specificity indicators are 92.4% and 99.15%, respectively.
10 ml of biological material (whole venous blood, plasma or serum) are transferred to a special recess on the surface of the test cassette. Then three drops of buffer solution are added to the blood. If the result is positive, purple stripes will appear in the test's area line. The time to get the result is 10 minutes.
The Russian test, characterized by high accuracy, is the express-VAC SARS-CoV-2-LFT, the first and currently the only domestic test system for rapid analysis for virus-neutralizing antibodies. The sensitivity of the test and its specificity are 95%. The reagents were tested on vaccines, primarily on Sputnik V. The kit includes an alcohol napkin, a sterile lancet and pipettes for transferring the biological sample. The principle of use is similar to the Korean test. The only difference is that any shade of the colour of the stripes should be considered positive. The result also appears after 10 minutes.
How often is it recommended to do tests for coronavirus
A retest for coronavirus should be passed regardless of what type of screening you used since any test system can show a false negative or false positive result. If there are symptoms of the disease after the first negative test, it is ineffective to repeat it immediately. The interval between testing should be at least a day so that the antibodies have time to form. If the symptoms are not observed, the test should be repeated after 10-11 days. For the same period (10-11 days), you need to focus on those who are sick with coronavirus and are waiting for the test to show a negative result. After receiving a negative result of a repeated test, you can calm down: you are healthy.Source: Snob. Read the original.