Updated 29 April 2021 With the COVID-19 pandemic, every day we hear about the different tests for the disease, circumstances in which are used, its goals and limitations. This subject is now part of our day-to-day conversations and we must be informed about, especially who decides on their own initiative (that is, without indication of health professionals) to test for COVID-19. Tests for COVID-19 The so-called rapid tests for COVID-19 have joined those we have known since the first wave of the disease, who need special equipment and laboratories, which are: PCR (polymerase chain reaction) tests or molecular tests, which search for ribonucleic acid (RNA) in the SARS-CoV-2 virus genome and tell us, in an appropriate clinical and epidemiological context, if there is, at the time of carrying out the test, a SARS-CoV-2 infection; Serological tests, which look for antibodies to the virus, and tell us whether there was an exposure to SARS-CoV-2 that our immune system tried to fight by producing antibodies, whether or not we had symptoms of the disease. What are rapid tests? Rapid tests are those whose results are obtained in a short period, usually minutes, and which do not need to be processed in a laboratory with specific equipment. Sometimes they are even carried out on the spot where the sample is taken. The best-known rapid tests are home pregnancy tests. Rapid tests for COVID-19 For COVID-19 there are: Rapid diagnostic tests, which aim to identify, in an appropriate clinical and epidemiological context, whether the virus is present in the organism when they are performed; Rapid antibody tests, which aim to identify whether there has been previous exposure to the virus and the body has developed antibodies. This article is about the first ones mentioned above, that is, the rapid diagnostic tests. The results of these tests interpreted in an appropriate clinical and epidemiological context, tell us if there is an active infection. They search for the presence of the virus, but do it differently from PCR tests: The rapid diagnostic tests for COVID-19 currently available for use on a large scale, screen for virus-specific proteins . These proteins on the surface of the virus are the viral antigen (which induces the immune response), so rapid tests are also known as antigen tests ; Tests that detect the SARS-CoV-2 antigen can even be performed at the same location where samples are taken and their results are available more quickly than PCR tests, which are performed in the laboratory and require special equipment. The technology that rapid tests use and the fact that they do not require laboratory processing makes them much cheaper than the PCR tests available today. The samples for the rapid tests of COVID-19 are globaly similar to those for the PCR tests: nasopharyngeal exudates obtained with a nasal and / or oral swab. Sensitivity of rapid diagnostic tests for COVID-19 Rapid tests are less sensitive than PCR tests and therefore the likelihood of obtaining false negative results is higher . Thus, as a rule, a negative result in a rapid test does not, by itself, exclude an infection by SARS-CoV-2 . The negative result must be assessed along with the rest of the clinical information and the epidemiological background of each person. Therefore, it may be necessary to perform a PCR test after a negative rapid test. This means that the degree of suspected infection is high and that the result of the rapid test could be a false negative. For their part, the PCR tests are very specific and sensitive, detecting very low levels of virus RNA in the samples with accuracy. False positives are rare and the rate of false negatives is much lower than that of rapid tests. The high sensitivity of the PCR tests even makes it detect SARS-CoV-2 RNA in the samples of nasopharyngeal secretions for several weeks after the onset of symptoms, despite the fact that the patient no longer has SARS-CoV-2 infection. The PCR laboratory test carried out using nasal exudate (nasopharyngeal) samples obtained by swab remains currently the initial diagnostic test of choice for SARS-CoV-2 infection . Proper use of rapid diagnostic tests for COVID-19 Although they do not have the sensitivity of PCR tests, rapid tests can be very useful, especially: In outbreak situations and for repeated testing of people in a known risk situation , with the aim of quickly identifying positive cases and isolating them to limit contagion; When the availability of PCR tests is limited and / or their results take too long for clinical needs ; For the diagnosis of symptomatic patients, in the initial stages of infection (onset of symptoms less than 5-7 days), when the virus replicates quickly and the likelihood of it in the body in high quantities is high. The possibility of carrying out rapid diagnistic tests in large numbers can thus help to control the pandemic, identifying and isolating the people who are most likely to spread the disease. We must also know In a pandemic context, when there is limited availability of tests and knowing that all tests can have false negative results (although some more than others), it is not uncommon, and is legitimate, for the diagnosis of covid-19 to be presumed based on the presence of symptoms and on risk of exposure (eg when there is transmission in the community) and that the same measures apply to people who test positive. References Caliendo AM, Hanson KD. Coronavirus disease 2019 (COVID-19): Diagnosis . Atualização de 30 de outubro de 2020. www.uptodate.com Guglielmi G. Fast coronavirus tests are coming . Nature 2020;585:496-7 Marshall WF. How do COVID-19 antibody tests differ from diagnostic tests? Mayo Clinic, 11/11/2020 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. To find out where you can do these tests, ways to book and other information, browse the pages: Covid-19 Drive Thru Test ; Covid-19 Quick Test ; Covid-19 test - antibodies ; Covid-19 Test PCR ; Covid-19 Traveler Test 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.
