"Quick test" is not a legally protected term. It can designate antibody tests, antigen tests or so-called LAMP tests.
LAMP tests and antigen tests detect the virus directly, which means that they prove the acute presence of the virus, whereas antibody tests detect the patient’s immune response to the virus and hence only show retrospectively that a person has been infected before.
Antibody test: It is necessary to take a blood sample in which antibodies as an immune response to the virus are detected. Usually an antibody test shows a positive result one week after the first symtomps occur; however, this period can also be longer and in some cases, no antibodies can be detected at all, although the patient has undergone an infection. Therefore, these tests are not appropriate in order to detect an infection. Furthermore, the quality of the available tests in terms of sensitivity and specificity varies greatly. In addition, it is currently not possible to tell via an antibody test whether a person is immune to the virus and would thus be protected against a second infection or not.
Antigen test: This test detects protein components of the virus in a sample (swab) taken from the throat or nose. There are two different techniques: In the fluorescence method, marked antibodies detect viral proteins contained in the sample. This detection leads – simply put – to a light signal which can be proven by a laboratory device. Furthermore, there are great hopes for antigen tests that work like pregnancy tests. In this case, the test strip changes its colour when viral proteins are contained in the sample.
In the meantime, the latter method has been further developed so that these antigen quick tests are now used regularly, e. g. in care facilities and integration service facilities. „Without cause“ means that there is no suspicion of a SARS-CoV-2 infection because the concerned person does not show any symptoms or has not been in contact with an infected person as far as this is known.
Series of tests without cause are carried out for particularly vulnerable groups, such as persons living and working in care facilities as well as their visitors. Since the antigen quick tests are currently not as reliable as the PCR tests (lower sensitivity and specificity), each positive test result must be confirmed via a PCR test or another evidence for nucleic acid. Thanks to the regular repetitions of the tests, the lower sensitivity is compensated in the context of test series without cause. In addition, according to the current state of knowledge, the viral load of an infected person showing a negative antigen quick test result is probably so low that the risk of infection for other persons is very limited.
LAMP Test: In a so-called LAMP Test (loop-mediated isothermal amplification), the genetic material is reproduced, similar to the PCR method. However, this procedure is a little bit quicker than many other conventional PCR procedures and at best does not even require any complex laboratory devices. Nevertheless, the validation regarding the sensitivity and the specificity of these test methods is not yet completely finalized.
Sensitivity: The sensitivity indicates how many infected persons are actually detected as being infected. When the sensitivity is 70%, this means that 30 out of 100 infected persons have falsely not been detected, but they feel safe and think that they are not infected.
Specificity: The specificity indicates how many non-infected persons have been detected as false positive. These persons must stay in quarantine and do another test again later. In the context of the current relatively low frequency of infections, a specificity of 98% already means that out of the persons with a positive test result, more persons have been tested falsely positive than correctly positive. Persons with a false positive result must stay in quarantine and do another test later.