Updated 15 November 2020 Both the ribonucleic acid (RNA) testing by real-time PCR and the serological tests, which we hear about every day related with the new coronavirus infection, are diagnostic tests . However, they look for different things, the PCR test looks for the virus, the serological test looks for antibodies against the virus. The results of both are important, whether to implement measures to contain COVID-19 , to learn about the disease or to make other public health decisions. The effectiveness of the two tests can vary, among other factors, with the stage in which they are performed. PCR tests for SARS-CoV-2 RNA screening PCR tests check whether the SARS-CoV-2 virus, which causes the disease known as COVID-19, is present in a sample. To do this, genetic material (ribonucleic acid, RNA or RNA) of the virus is searched. If RNA of the virus is identified in a sample it means that the virus, or remains of it, is present and, therefore, with appropriate clinical and epidemiological context, that there was an active infection when the sample was collected. PCR stands for polymerase chain reaction. The sample for these tests for the SARS-CoV-2 virus is the nasopharyngeal exudate taken with a swab. The correct collection of the samples is decisive, namely for not obtaining false negative results because an insufficient sample was collected. Thus, the PCR test: Search for the virus; It may tell whether at any given moment there is an active infection; Helps to identify people who can infect others and, therefore, to guide the implementation of isolation and protection measures to contain the infection; Contributes to characterize the disease, for example to know how the infection is spread, its severity in different age groups, the relationship between severity and the presence of other diseases. Serological tests for antibodies against SARS-CoV-2 Serological tests look for evidence of the SARS-CoV-2 virus being in the body. To do this, it checks whether antibodies against this virus are present in the serum obtained from a blood sample. To perform these tests, different techniques can be used, one of which is known as ELISA, which means enzyme-linked immuno-assay. The production of antibodies is part of the defense mechanisms of our immune system against agressors (antigens), for example, viruses, bacteria, fungi, parasites. Antibodies are specific proteins (immunoglobulins or Ig) produced to fight infections. Antibodies are not all the same, they do not all form at the same stage after infection and their levels are maintained for different periods. Thus, if there are antibodies to the SARS-CoV-2 virus in a sample, it means that there was an exposure or contact with the SARS-CoV-2 virus and an immune response to that exposure. The results of serological tests can also make an important contribution to better know the disease. However, as COVID-19 is a new disease there are limitations because it is still largely unknown, for example: How IgM and IgG antibodies (seroconversion profile) evolve after exposure to the virus; If these antibodies confer immunity to a new infection, that is, if you are resistant / immune to the development of a new infection if you will be exposed to the virus again; In the case of conferring immunity, what is the level of antibodies (antibody titer) that is protective against a new infection and how long does protection lasts. Thus, the serological test: Says if there was an infection with the coronavirus and if the immune system tried to fight it; It allows to identify people who have had an infection, even if they have not had symptoms of the disease; It may help to identify who is immune to the infection and when the infection occurred; It can help to know the spread and evolution of the disease in a population, as well as their immune status. Author : Betânia Ferreira In most of the hospitals of Hospital da Luz network it is possible to perform tests for COVID-19 , both for travelers and other tests. Browse the pages Covid-19 Test , Covid-19 Drive Thru Test e Covid-19 Traveler Test , to find out where you can do these tests, ways to book and other information. Click here for more information and advice of Hospital da Luz about the novel coronavírus COVID-19 epidemic . The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
