The serological test determines if there are specific antibodies against the coronavirus SARS-CoV-2 in your blood. The test shows if you have had the virus. Antibodies are part of your natural defences: the immune system. The body produces them in response to an infection with the virus. It can take 2 to 3 weeks for your body to produce the right antibodies and release them in sufficient quantities in your blood, so they can be detected. A serological test involves taking a blood sample. This test is primarily used for research and screening at the population level, by selected laboratories. This test is not suitable to check if you have the virus now. In exceptional situations, the serological test is also used in hospitals. It may be used if someone is improving very slowly, or if someone develops more symptoms again after an initial improvement.
Immunity and protection
Serological tests are used to estimate how many people in the Netherlands were previously infected with the virus, and whether people are building up and retaining immunity to the virus. RIVMNational Institute for Public Health and the Environment
is researching these topics in the PIENTER Corona Study, among others. In doing so, RIVM is collecting information about the number of people who have been in contact with the virus.
It is not yet known how long antibodies against the virus remain present in your blood. Also, it is not yet known whether detecting the presence of antibodies offers any certainty that you are immune and protected, or how long you may be protected. So far, it has been confirmed that a limited number of people have been infected for a second time.
Commercial, ‘off the shelf’ rapid serological tests are unreliable
Planning to buy a serological test or ‘rapid diagnostic test’ from a commercial provider to see if you already had the virus? That is not a good idea. Many of these ‘rapid serological tests’ are being sold that promise to show if you have already had COVID-19 based on a droplet of blood. Research shows that these tests are not reliable. These tests do not work well on people who have not been seriously ill. Also, they do not work on people who are just developing their first symptoms. The World Health Organization also discourages the use of rapid serological tests.