Rapid antigen tests are very reliable at detecting whether someone has a high viral load and is therefore very infectious. This applies to both the antigen self-tests that you do at home and the rapid antigen tests done at testing sites.

But when only low levels of virus are present, as is the case in the first few days of an infection or when a vaccinated person becomes infected, antigen tests are less reliable because they are often not sufficiently sensitive to detect small amounts of virus. So the result can be a false-negative.

An additional factor is that the sensitivity of the tests varies depending on the manufacturer and the product. Some tests detect small amounts of virus while others do not. The Paul Ehrlich Institute (PEI) has tested the sensitivity of 122 antigen tests available on the market and published the results here.

Another reason for incorrect results is that mistakes are often made in the testing procedure.  So before you do a home test please read the instructions carefully and stick to the procedure exactly.

It is also possible for a rapid test to yield a false positive result. In this case, following it up with a PCR test is the only way to find out with certainty whether an infection with SARS-CoV-2 is present or not.

Further information about COVID tests is available at infektionsschutz.de, the website of BZgA (the Federal Centre for Health Education).

The Paul Ehrlich Institute (PEI) provides further information on the sensitivity of rapid antigen tests.

Detailed instructions on the use of self-tests are available from the Robert Koch Institute.

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