Home tests for COVID-19. How to do them? What mistakes to avoid?

In pharmacies, you can find many tests to detect the presence of COVID-19 at home. The test material may be a nasal or throat swab, as well as a saliva sample. There are also tests for antibodies that tell about a history of illness or contact with the virus. Which tests to choose? What does the testing process look like and what errors should be avoided? For MedTvoiLokona, doctor Bartosz Fiałek is explaining.

1. The rapid antigen test detects the presence of the SARS-CoV-2 coronavirus antigen in the human body
2. It is a very practical test because – for comparison – in the case of a PCR test, the result may remain positive longer than we are infectious – says doctor Bartosz Fiałek
3. Not all tests detecting the presence of virus from saliva are adequately standardized – adds Fiałek
4. As the doctor points out, it is safest to perform the test on the fifth day after contact with a potentially infected person
5. More information can be found on the Onet homepage

Nasal / throat antigen test for COVID-19

A quick test to detect the presence of the SARS-CoV-2 coronavirus antigen in the human body is a popular diagnostic method. It is recommended for people who show typical symptoms of coronavirus infection, such as fever, cough, runny nose, shortness of breath, sore throat or muscle pain, but it can also be performed by people who have no symptoms but suspect contact with an infected person.

The test can be done at home by taking a swab from the front of the nose (pharynx, nasopharynx). The swab should be rotated for several seconds, rubbing it against the nasal mucosa, then insert it into the test tube with the liquid (reagents), shake it, take the swab out, and place a few drops of the liquid in the test device.

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We get the result after a few or a dozen minutes (up to half an hour). A visible control line together with a visible test line indicate a positive result. When this occurs, contact your doctor who may order a PCR test. You can also self-report the need for a test on the government website dedicated to coronavirus.

The test can be used by children and adults, including pregnant and breastfeeding women.

Bartosz Fiałek, a doctor, on antigen tests from the nose / throat:

Bow. Bartosz Fiałek

Antigen tests for the presence of SARS-CoV-2 infection must be at least 80 percent. sensitivity and 97 percent. specificity so that they can be introduced to the general market. Such guidelines were presented by the World Health Organization. They are a very good solution for the proper performance of the test. Antigen tests correspond well to the times when we can infect others from the environment due to the high viral load. The problem is that this test will not detect exactly when we are infectious. In the case of the Omikron variant, we talk about two days when we are infectious, and on average, on the third day, we obtain a positive antigen test result for the presence of new coronavirus infection.

Antigen tests detect – as the name suggests – antigens in the collected biological material, in this case from a swab from the back wall of the nasopharynx. If, during the test, in the assessed material, we have too few copies of the virus, because it has not multiplied yet for the test to detect it, but there is already enough of it that we are contagious to the environment, then we see a “window” between the moment when we already infect and not yet the test shows us a negative result. However, since a positive result for the presence of SARS-CoV-2 infection, subsequent antigen tests have correlated with the time of infectivity. When after a few days (6-7) of obtaining a positive result, two subsequent results are negative, we can say with high probability that we are no longer contagious. This is a very practical test, because in comparison with a PCR test, the result may remain positive longer than we are infectious.

It is estimated that most antigen tests will not detect infections below 500. copies of the virus, and PCR tests are positive as early as 200 copies of the virus per milliliter. This difference makes PCR tests positive faster, but also negative later than antigen tests. Therefore, in determining the infectivity of the here and now, and release from quarantine or isolation, antigen tests seem to be better.

Saliva antigen test for COVID-19

This is a rapid immunoassay that detects the presence of the SARS-CoV-2 coronavirus antigen in a sample of human saliva. The indication for the test is the presence of symptoms that may suggest infection with the coronavirus, as well as suspected contact with a person suffering from COVID-19.

You can do the test yourself at home by collecting the right amount of saliva and placing it in a test tube. Saliva should not be “fresh”, manufacturers recommend coughing a few times before spitting the saliva sample through the test tube funnel. Then, add the buffer fluid to the test tube with saliva, mix the contents, and then place two drops of the solution in the test device.

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We get the result after 15 minutes. A positive result is shown by a visible control line (C) together with a visible test line (T). According to the manufacturers, this is only a preliminary result, which should be confirmed by the result of clinical diagnostics. Therefore, in the event of positive results, contact your primary care physician who will recommend the next steps.

The test can be used in children and adults, including pregnant and breastfeeding women.

You can buy SARS-COV-2 smear antigen test for self-monitoring at an attractive price on Medonet Market.

Bartosz Fiałek, a physician on antigenic saliva tests:

Bow. Bartosz Fiałek

In the case of tests for the presence of new saliva coronavirus infection, not all of them are adequately standardized. At the moment, research is being carried out on the parameters and reliability of tests for the presence of SARS-CoV-2 infection, for which saliva is the biological material. The available scientific data indicate that these are very reliable tests, sometimes with a reliability comparable to PCR tests, especially in the era of the Omikron variant, which multiplies more often in the upper respiratory tract, mainly in the throat, then in the nasal cavities, compared to the Delta variant. . I believe that they will have significant application in the future, but at the moment one preference is given to swabbing the posterior nasopharyngeal wall (possibly for children who cannot tolerate nasal swabs, try using the saliva test).

Current global recommendations do not recommend widespread testing for the presence of SARS-CoV-2 infection from saliva. The standard is still to make a smear from the back wall of the nasopharynx, possibly from the throat and nose. Nevertheless, saliva testing is an excellent idea that can be especially useful in case of infection with variants that multiply in the upper respiratory tract.

A blood antibody test for COVID-19

An immunoassay that detects IgG and IgM antibodies that fight coronaviruses. Importantly, the test does not indicate the presence of the virus itself in our body.

The test material is blood taken from the finger. Using a pipette, take a solid drop from the previously punctured finger and place it on the test, and then drop a few drops of the reagent there. We get the result after a few or a dozen or so minutes.

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A positive result is indicated by the color of the lines indicating IgG and IgM antibodies. When the result is negative, only the control area becomes stained.

After confirming a positive result, it is necessary to consult a doctor who may order a PCR test. You can also independently report the need for such a test on the government website dedicated to coronavirus.

The test is safe for children and pregnant women.

You can order the COVID-19 SGTi-flex cassette test today at Medonet Market.

Doctor Bartosz Fiałek on antibody tests:

Bow. Bartosz Fiałek

Antigen tests tell us about something other than antibody tests. Antigenic ones detect active infection, and antibody tests detect previous contact with the virus, COVID-19 infection or vaccination, depending on which SARS-CoV-2 protein they are tested against. This is a big difference in the context of what question we want to answer: is a given condition the result of exposure to a wild virus or vaccination, is it an active disease and the moment when we are contagious to the environment.

Tests for the presence of antibodies against SARS-CoV-2 will tell us nothing special in the clinical context, with single exceptions. As a person faithful to performing additional tests for specific indications, I believe that – as the name suggests – we perform certain tests as an add-on to detail our suspicions in order to make a specific clinical decision. The titer of anti-SARS-CoV-2 antibodies, which we obtain after performing the test for their presence, regardless of whether they are anti-S or anti-N, does not affect any of the important clinical decisions, or whether it is still we are protected after being infected or vaccinated, or to make a decision on the basis of a specific dose of the COVID-19 vaccine — here the time elapsed since receiving the previous one decides.

Therefore, at the moment such a test has an academic sense, rather than a clinical, civic sense. I do not recommend such tests. The exception are people who are immunocompetent (those who are not able to produce an adequate immune response – ed.). In their case, such a test may be ordered to assess the response to vaccination in detail, but in case of doubt, it should be done by the treating physician, not the patient himself.

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The rest of the text is below the video.

Home antigen test – when to perform?

Adrian Dąbek, Medonet: What is the best time to perform an antigen test? Immediately after noticing symptoms?

Bow. Bartosz Fiałek: At the beginning of the COVID-19 pandemic, it was said to be five – seven days from contact, for the Delta variant it was four – five days, and for the Omikron variant, it was said to be an average of three days from potential exposure to the virus. We can, of course, perform such a test after a day of contact, but we must take into account that a negative result will not give us certainty and we will have to repeat the test. We should take into account that more than one antigen test will have to be performed. It seems that on average three days after contact, we already have enough copies of the virus that the antigen test will be positive. More specifically, in the context of the Omikron variant, two or four days from the contact are referred to. The safest – and this is what global recommendations say – is to perform the test on the fifth day after contact, if previous tests were negative and there is a suspicion that we may be infected.

However, it should be remembered that by the fifth day we should behave as if we are potentially sick with COVID-19, so we should avoid clusters of people, and when leaving the house, we should wear a mask, because even if we do not have symptoms, we can already be infected. The fifth day is now the standard that will allow us to assess our epidemiological status. If we are negative, it is very likely that we are not infected, and if we are positive — we are sick. An earlier negative test will have to be repeated.

Home antigen test – what mistakes to avoid?

What should we pay attention to when performing the test. What could cause it to be performed incorrectly?

We should not smoke cigarettes, eat heavy meals, use nasal antimicrobial preparations two hours before the test. The antigen test is a diagnostic test, which means that we should prepare for it properly. Before the blood test, we also have specific preparation recommendations.

As for the performance itself, we should strictly follow the instructions in the leaflet. The stick, i.e. the swab, should be inserted deeply so that the swab is actually taken from the back wall of the nasopharynx, and not from the nasal vestibule, because incorrect collection of biological material for testing may result in an unreliable result (false negative or false positive).

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In the leaflet of each antigen test, and I have seen many of them, it is indicated how to insert the swab into the nasopharynx and how to take the swab, e.g. how long to rotate it. The principle of taking a smear is similar, but not always the same, in all tests. In general, it is a really simple procedure and if we do it as shown in the leaflet, the result will be reliable.

Be aware that antigen tests are not 100% reliable, so there is a risk of both false positives and false negatives. However, if a given test meets the minimum approval criteria (sensitivity 80%, specificity 97%), we will detect the vast majority of infections with them.

At the beginning there were signals that Omikron was escaping antigen tests.

It’s not true. The antigen test is based on the virus load in the tested biological material, i.e. the number of virus copies. If there are less than 500, the result may be negative. The genetic test detects the infection earlier because it is positive already with fewer copies of the pathogen. Initial doubts were caused by the fact that in the case of infection with the Omikron variant, the viral load is lower than in the case of the Delta variant. Hence, a positive result of the test for the presence of infection with the Omikron variant could appear later compared to the Delta variant.

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