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Covid-19 How do you use the corona rapid tests correctly?

Do I have Corona and should I go into quarantine - or is it just a harmless cold? Only a test can provide a reliable answer to this question, but access to it has been limited so far. Only those who had close contact with a confirmed infected person and showed symptoms themselves were given a test. But now corona rapid tests for at home should bring enough test options for everyone. However, many people still have questions: How do you use the test sets correctly? And will the test result be positive even if I have just been vaccinated?

Vaccination does not lead to false test results

Corona tests for private use have been available in various countries around the world since last year. Often, however, they were considered unreliable. Only newer tests should now bring more reliable results. The Federal Institute for Drugs and Medical Devices (BfArM) is gradually allowing tests for free sale. The current list of approved tests can be found here.

These are so-called antigen tests. You can detect certain proteins of the coronavirus in a sample. Usually the nucleocapsid protein (N-protein) of Corona is searched for. Because the samples for the rapid tests are taken in the upper respiratory tract, virus protein must be present there in order to produce a positive test result. However, this protein can only get into the nose, throat and throat with the virus, not with a vaccination.

The virus antigens formed by the vaccination only occur in lymph nodes near the puncture site, i.e. in muscle tissue. They don't get into the throat and nose. If a rapid test is positive despite the vaccination, it is possible that a vaccinated person has contracted the coronavirus anyway.

Negative test results do not offer 100 percent certainty

The Paul Ehrlich Institute responsible for drug safety has evaluated various antigen tests and published a list listing all tests that passed the evaluation. The tests now approved for private use must have passed this check. A prerequisite for this is that they can be carried out easily by laypeople.

All tests are considered to be relatively reliable. Relative, because: If the viral load in an infected person is very low, the rapid test may not work. Such cases are still best discovered using the PCR test. A negative rapid test result does not offer 100 percent certainty that someone is not at risk of infection. To ensure that an infection is not overlooked, it is also important that the smear is taken correctly.

It all depends on the right smear technique

How the tests are to be carried out is set out in the relevant accompanying notes. "The swabs must be taken exactly as the manufacturer says; the rapid tests are only approved for this," says Professor Bettina Löffler, director of the Institute for Microbiology at the Jena University Hospital. Her Dresden colleague Katja de With adds:

However, the rapid antigen tests are getting better and better and according to the BfArM, some are already approved as medical products that also allow smears from the anterior nasal area or from spit. These detect virus proteins, the nucleocapsid protein (N protein), so that mutations in the spike protein (S protein) do not affect the function of the test. A positive rapid test should be confirmed by a PCR.

Dr. Katja de With, Head of Clinical Infectious Diseases, Dresden University Hospital

According to a spokesman for the Federal Institute for Drugs and Medical Devices (BfArM), rapid tests may have different instructions, depending on whether they are sold to medical institutions and thus to professionals, or whether they are intended for private use. "The prerequisite for sales to private users is that the tests are carried out safely by these people," says Maik Pommer from the BfArM. A safe implementation means that the smear must not be so difficult or uncomfortable that users would certainly make mistakes.

The different smear methods

For a deep nasopharynx swab, the sterile cotton swab included in the set must be inserted deep through a nostril, pushed up to the throat area and turned several times. This is the smear method recommended to professionals. You can also try it for private users. The advantage is that most of the mucus and therefore the safest virus material is found in the nasopharynx when an infection is present.

However, the throat swab should be more pleasant. The stick should be inserted through the mouth and stroked three to four times over the tonsils at the back of the throat. For a simple nasal swab, on the other hand, the cotton swab should be inserted three to four centimeters into one nostril and turned around five times before the procedure is repeated with the same cotton swab in the other nostril. The respective package insert indicates which reductions are possible.