COVID-19 antigen test: advantages of rapid method and instructions

The rapid coronavirus test has many advantages. It helps to quickly detect the presence of the virus and protect people around you, especially those at risk, from possible infection. In order to navigate through the large number of different tests, you need to determine what it is for and when you need to take the test.
What are the rapid tests for COVID-19

Today, the presence of SARS-CoV-2, the virus that causes COVID-19, is determined using two techniques:

- PCR test;

- Express antigen test.

PCR Tests

PCR or polymerase chain reaction is a method of molecular diagnosis. It detects the RNA of the virus in the body and allows you to know if a person is currently sick or a carrier. The accuracy of this method is quite high and is almost 100%. But the final result of the test is affected by careful preparation of the material.

PCR tests for coronavirus (RT-PCR) should always be given to those who have returned from abroad, had contact with patients with coronavirus, as well as patients diagnosed with community-acquired pneumonia, acute respiratory viral infection and influenza, employees of medical institutions and people over 65 years - they are in the risk group.

You can have a PCR test in a state polyclinic (if you have an MHI policy) and in private laboratories. The important condition is the absence of obvious signs of cold and contact with sick people in the last few days. For the COVID-19 test, biological material from the oropharynx and nasal cavity is taken as an outpatient or a specialist can come to the house. It is then tested in a laboratory using special equipment, and you have to wait at least 24 hours for the results.

Фото: Unsplash

Antigen Tests

The antigen tests (RAT) detect the proteins of the virus. Using small disposable plastic cassettes, the presence of the genetic material of the virus is determined in a similar way to laboratory methods. The advantage of this method is that the test is carried out with small devices that can be easily transported and set up outside of a specialized laboratory. In this case samples from the nose or throat are also examined. The analysis is based on the detection of the virus antigen and takes between 5 and 30 minutes.

The first test systems had a high error rate, but today's modern test models are quite accurate. If the test is taken correctly, the reliability of the results is over 80%.

Today express testing is considered a convenient and quick way to determine the presence of the virus in the body. Test systems are used in airports, train stations, large enterprises and medical institutions. The analysis requires minimal preparation and is much cheaper than PCR testing.

Benefits of COVID-19 rapid tests

Rapid tests are done in medical facilities to confirm or rule out COVID-19 infection in people with or without symptoms. Such tests:

    Portable, they can be used anywhere;
    easy to perform, with minimal additional equipment or a minimum of complicated preparatory steps;
    are cheaper than standard laboratory tests;
    Do not require special equipment and conditions;
    provide results quickly.

Patients with suspected COVID-19 should learn quickly about the possible presence of infection in order to receive treatment to inform those in close contact. Most often, coronavirus infection is confirmed by PCR test, but as mentioned above, it requires special equipment and at least 24 hours to obtain results.

Express tests for the antigen at medical offices can test a much larger number of people. In addition, the test can be done not only in specialized medical facilities. Provided the results are accurate, a faster diagnosis will allow patients to take the necessary steps more quickly and reduce the spread of COVID-19.

Фото: пресс-служба

 

Rapid antigen testing as an alternative to PCR tests

Scientists at the Institute of Microbiology in Lausanne conducted a study: they introduced SARS-CoV-2 antigen testing in the emergency department of a Swiss university hospital. The sensitivity of the tests and the accuracy of the results of the experiment were tested on 532 patients. The scientists compared the most popular and available rapid antigen tests with PCR.

As a result, they concluded that RAT could be a useful resource in selected clinical settings as a complementary tool to PCR. It would help with rapid triage of patients, especially during a disease outbreak. But the lower sensitivity of the test must be considered, especially in asymptomatic patients.

The study also found which antigen tests give the most accurate results. Scientists analyzed the most popular and commercially available samples. During the experiment, PBCheck Covid 19 Ag showed the best results compared to analogues. This test has a high accuracy of 88.5%. At the same time, this indicator for Panbio Covid-19 Ag Rapid Test was 87%, and for Standard Q and BD Veritor - 87.2%.

The use of rapid antigen tests in Switzerland helped cope with the next wave of the pandemic. Sorting patients by them allowed Swiss specialists to quickly isolate patients who tested positive for COVID-19 and save resources. That is why many European countries now choose rapid antigen tests as a guarantee of epidemiological safety.

PBCheck Covid 19 Ag test was also tested in Russia. Reagent kits were used for this purpose, using 35 positive and 35 negative clinical samples of biological material (nasal and oral smears). The following diagnostic characteristics were established during the experiment: diagnostic specificity 100%, diagnostic sensitivity 92.11%.

Фото: пресс-служба

How to do the antigen test

A rapid antigen test is a fairly convenient method of diagnosing SARS-CoV-2 because it allows you to test for the infection in a large number of people as quickly as possible.

Coronavirus antigens can be detected in the contents of the nasopharynx by immunochromatographic analysis. To do this, you need to take a swab. Here are instructions on how to do this correctly:

    Insert a sterile swab into the nasal cavity and gently push it up to the nasopharynx;
    Make several rotating motions with the swab and remove it. Take care not to touch the bottom of the nasal septum;
    dip the swab with nasopharyngeal secretion into a tube of extraction buffer;
    Pressing the swab against the inner walls of the tube, perform several rotations with it. Then move the swab up and down;
    Remove the swab by exerting pressure on the side walls of the tube so that as much of the test material remains in it as possible;
    put the drip cap on the tube and squeeze two drops onto the test cassette;
    wait for 10 minutes and then start determining the results. It is important to remember that after more than 15 minutes, the result may be distorted due to the contact of the reagents with the air. In this case it will be invalid;
    Make sure that there is a colored bar on the reference line C. If it is absent, the test result is incorrect;
    Pay attention to the T line: the presence of pink or red stripe indicates a positive test result. In this case you need to consult a physician. The absence of a strip on the T line indicates a negative test result. Your smear does not show COVID-19 antigen.

Фото: пресс-служба

Expert Commentary: Zhanna Sapozhkova, head of the Laboratory Hemoskrin, PhD, head of the International School of Cytology (ISC, Moscow); author of more than 40 scientific publications; editor-in-chief of ISC training programs for accreditation in NMO; corresponding member of the International Academy of Cytology / MIAC.

What is the accuracy rate of modern rapid tests for Covid? How accurate are the results?

In the diagnosis of an infection as serious and socially significant as COVID-19, accuracy and high specificity are important. That is, the tests should detect even small amounts of the virus and should not diagnose other infections. Virtually all current tests for the diagnosis of coronavirus infection meet the requirements of high sensitivity and specificity.

For example, the PBCheck COVID-19 Ag test that our laboratory works with has a specificity of 100%, which means that it will not diagnose any other infections but the coronavirus one, and its sensitivity is 92.11%, which means that out of 100 infected people, 92 will have the virus detected. The remaining 8 could be, for example, low-copy samples, that is, those samples where the amount of virus is negligible.

Can the antigen test be used equally instead of the PCR test?

Rather on an equal footing with the PCR test. This is the case in many European countries. You can buy a test in pharmacies, do it yourself, bring the result and get a certificate to travel to another country. Europe validates the rapid tests and marks them with the CE mark (indicating that the products meet the standards and provide free admission of goods to the markets of all EU countries. - "RBC Style"). Our European colleagues believe that express testing will be one of the possible factors that will help to survive the next wave of coronavirus.

In what situations would the use of an antigen test be preferable to PCR?

These are situations where the test is needed quickly, such as testing at events or if a relative comes to the hospital to visit a patient. In these cases, rapid tests are incomparably better than PCR, as they give a quick answer with the same quality of testing. Another situation is when, for example, there are symptoms and the PCR test is negative. In this case, the use of an express test can help identify the infection.

If the antigen test is much easier and faster, is there a possibility that it will replace the traditional PCR test in the future?

As far as I can see the development of diagnostics in the last ten years, laboratory tests are becoming more diverse and faster. Rapid testing refers to POC testing (point of care), it allows to exclude or confirm a disease timely, quickly and qualitatively, and thus to take the necessary treatment or preventive measures in time. So the future is undoubtedly in rapid tests.

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