Rapid tests and COVID-19

At a time when the new coronavirus pandemic continues to advance in Brazil and in the world, the need for massive tests to detect the disease and to know the true number of infected people is growing. An accurate and correct diagnosis is essential to propose any measure related to the prevention and prognosis of infections.

The gold standard technique, considered the most accurate for diagnosis, is RT-PCR (an acronym for reverse transcription followed by polymerase chain reaction). It consists of the detection of viral RNA sequences. The test has the disadvantage of requiring a few days to be processed and the report must be issued by the laboratory.

Serological tests, on the other hand, detect the presence of class M (IgM) and G (IgG) immunoglobulins, produced by the body in response to infection by the virus. IgM is the main immunoglobulin that is formed after infection and begins to be detected between days 3 and 5 after infection, with a detection peak after the seventh day. As the infection progresses, IgM levels decrease and, conversely, IgG levels increase rapidly, with maximum detection after day 14 of infection.

The rapid test can be performed on whole blood, serum or plasma samples and the result will be available in approximately 15 minutes. The possibility of infection, however, cannot be ruled out with a negative result. This is because the production of antibodies, at the beginning of the disease, may not have been detected by TR, which caused the false negative. In such cases, it is suggested to repeat the test, to confirm, or not, the absence of infection. In addition, rapid tests can identify if the person has been previously infected, even without experiencing symptoms.

Rapid tests play an important role in understanding the dynamics of virus transmission in the population and in identifying groups at high risk of infection. They can also determine the proportion of the population that has been infected, helping to identify which communities have had a high rate of infection.