General Practice 2022

RT-PCR for COVID-19: when to do it and results

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RT-PCR for COVID-19: when to do it and results
RT-PCR for COVID-19: when to do it and results
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The PCR test, also known as RT-PCR, is an extremely sensitive laboratory test that is done to identify the presence of a specific type of genetic material in the collected sample. This test is often used to identify virus infections such as Zika, Ebola, H1N1 or, more recently, COVID-19.

In the case of COVID-19, this test is done to identify the presence of genetic material from SARS-CoV-2, which is the virus responsible for the disease. Thus, when the result of the RT-PCR test is positive, it means that the person is infected, being diagnosed with COVID-19.

PCR is used as the standard for diagnosing COVID-19 and should be performed when a person has symptoms of suspected infection or has been in close contact with an infected person.

When to take the PCR test for COVID-19

PCR is indicated whenever there is a need to confirm or rule out the diagnosis of COVID-19. Thus, it is indicated in the following situations:

  • Presence of suspicious symptoms of COVID-19, especially from the 3rd day onwards, such as dry cough, fever, tiredness, sore throat and loss of taste, for example;
  • Rapid antigen test for COVID-19 with positive result, even in people without symptoms;
  • Recent close contact with people infected with COVID-19, even without symptoms.

The RT-PCR test for COVID-19 may also be required before surgery or hospitalization, to rule out a possible asymptomatic infection and ensure the safety of hospitalized people, in addition to being requested before performing a travel by plane, normally being indicated 48 to 72 hours before boarding.

How the exam is done

The PCR test to detect COVID-19 infection is performed by collecting nasopharyngeal (back of the nose) and/or oropharyngeal (back of the throat) secretions, using a swab, which is similar to a long cotton swab.

The collected sample is then packaged and sent to the laboratory for analysis, where it is placed in a special device that detects the presence of the genetic material of the COVID-19 virus.

How to understand the result

The result of the PCR exam can take up to 3 days to be ready, but in most cases it is released in less than 24 hours. The result could be:

  • Positive/detectable: means that SARS-CoV-2 genetic material has been identified in the sample and, therefore, the person has an active infection, being diagnosed with COVID-19 19;
  • Negative/not detectable: Indicates that SARS-CoV-2 genetic material has not been identified and therefore the person does not have an active COVID-19 infection.

In cases where the RT-PCR test gave a negative result, but the person had close contact with someone infected, it is recommended that isolation be maintained for up to 14 days, even if there are no symptoms, as you can still develop the infection. However, if the person begins to show symptoms suggestive of COVID-19, they should repeat the test to confirm the diagnosis.

A negative result also does not mean that you can stop using preventive measures, such as frequent hand washing, distancing and wearing masks. This is because there are cases in which the result is negative, but the person is at a very early stage of the infection where it is difficult to identify the genetic material of the virus. Check out all the prevention measures against COVID-19.

In cases of positive result, isolation should be carried out to avoid passing the virus to other people, monitoring symptoms to assess whether they are worsening and starting treatment if necessary.See how COVID-19 is treated. It's also important to notify people who have been in close contact in the last 14 days so they can take a quick test and be aware of the possibility of being infected.

When not to take the PCR exam

The RT-PCR test for COVID-19 should not be performed in cases where it is intended to know if you have already been infected with COVID-19 or if you have antibodies to the disease, after vaccination, for example. This is because the PCR exam only identifies an infection that is active at the time of collection. In such cases, it is advisable to do a rapid antibody test, which analyzes a small sample of blood. Understand how this test works.

What to do in case of COVID-19

If you have a positive COVID test, have symptoms suggestive of the infection or have been in contact with someone infected, please fill in your details to find out what to do:

  • option=b, @block-A1"' > I tested positive for COVID-19.
  • option=c, @block-A1"' > I have symptoms suggestive of COVID-19.
  • option=d, @block-A1"' > I've been in contact with positive case.
  • option=f, @block-F1"' > I've had COVID-19, but I still have symptoms.
  • option=e, @block-A1"' > I want to know more information.
  • country=en, @block-B1"}, {"condition":"option=c", "action":">country=en, @block-C1"}, {"condition":"option=d", "action":">country=en, @block-D2"}, {"condition":"option=e", "action":">country=en, @block-E1"}]' > Portugal
  • country=br, @block-B1"}, {"condition":"option=c", "action":">country=br, @block-C1"}, {"condition":"option=d", "action":">country=br, @block-D1"}, {"condition":"option=e", "action":">country=br, @block-E1"}]' >
  • Self-test.
  • Rapid antigen test.
  • RT-PCR.
  • Restart

    • I have no symptoms.
    • I only have mild symptoms (fever, cough, tiredness, headache, sore throat, loss of tasteā€¦).
    • I have moderate symptoms (very intense cough, some shortness of breath, excessive tirednessā€¦).
    • I'm really short of breath.
    • Restart

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    • No.
    • I did a self-test
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    • I did RT-PCR test.
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    • test=0"' > Negative
    • test=1"' > Positive
    • Restart

      It is possible that your symptoms are a sign of another infection, such as the flu or H3N2, for example. Still, we advise you to repeat the COVID-19 test within the next 3 days. Check out the differences between flu, COVID-19 and a cold.

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    • risk=1, @block-D5"' > I live with the person who tested positive.
    • I have been in direct contact with the positive person (less than 2 meters) for more than 15 minutes and I am a he alth professional or work in an institution for the elderly.
    • risk=0"' > The person who tests positive does not live with me.
    • Restart

      • Yes.
      • No.

      Your contact is considered high risk. You do not need to isolate yourself, but you must maintain all personal protective measures for 14 days, be aware of the appearance of symptoms and perform a COVID test as soon as possible (rapid test or RT-PCR).If the result of the 1st test is negative, you must repeat the test between the 3rd and 5th day after contact with the positive person.

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    Your contact is considered low risk. For this reason, you don't need to do isolation, or perform COVID test. However, you must maintain all individual protection measures (such as wearing a mask and avoiding unnecessary travel) and be aware of the appearance of symptoms in the next 14 days.

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