So far, the so-called polymerase chain reaction (PCR) has been used to detect a coronavirus infection. The method delivers reliable test results within up to five hours, but often a lot of valuable time passes when the samples are sent to specialist laboratories. Time in which infected people can infect other people without a diagnosis. Researchers, laboratories, and various manufacturers are working on new methods, including rapid tests, in order to be able to test more patients for the new coronavirus more quickly.
Antibody tests detect virus-specific antibodies and show that someone has been in contact with a virus. The problem is antibody tests only detect a reaction of the immune system to the virus, not the virus itself. They do not indicate acute infections, but only those that have already survived – but only about two to three weeks after infection. Almost all antibody tests react wrongly positive if you have normal coronaviruses, which are four types of classic cold viruses. The antibody tests that are already used in specialist laboratories also have an error rate of around two to three percent, which means that for every 100 tests there are at least two false-positive results. Test results from antibody rapid tests should be checked with so-called neutralization tests. However, these are so complex that they cannot be carried out for the entire population. So far, COVID-19 antibody test have not been able to replace the reliable PCR test.
The polymerase chain reaction (PCR)
So far, the PCR method (polymerase chain reaction) has been the most reliable “COVID-19 test methods”, but only specialist laboratories can carry it out. For the polymerase chain reaction, swabs or samples are taken from the mouth, throat, nose, or bronchi and subjected to a chemical process. For this, pieces of DNA are copied and multiplied in order to search for special pieces of DNA, for example of the coronavirus. This means that there is always a clear search order at the beginning, a clear diagnostic question. Then a selected piece of DNA is copied, heated, cooled, and finally energized in a medium in a special machine.
The polymerase chain reaction is also suitable for detecting viruses, bacteria, and parasites in infectious diseases. The procedure also shows how many pathogens are in the body. With virus infections, this is called the “viral load”.
Cartridge tests are actually rapid tests using the PCR method that can be carried out outside of laboratories. To do this, cartridges with airway samples are placed in a device with a fully automatic analysis system. After about an hour, the result is there because you don’t have to work in several steps as with the classic PCR method. The problem is cartridge systems work reliably but are so expensive that only laboratories can usually afford them.
Antigen tests are still in development and are designed to detect viral proteins, i.e. fragments of a virus, in samples (deep throat swabs). Acute infections could be detected in this way. As with antibody tests, there is a problem that false-positive results can result if you are only infected with the common cold coronaviruses, not the new coronavirus.