PCR test: what it is, what it is for and results

The PCR test, or RT-PCR, is an extremely sensitive laboratory test that is widely used to confirm the existence of virus infections, such as Zika, Ebola, H1N1 and, more recently, COVID-19.

In addition to viral infections, the PCR test may also be indicated to investigate some bacterial infections, the presence of mutations in DNA that may increase the risk of cancer or to monitor the evolution of the disease and response to treatment.

The PCR test can be carried out using various biological samples, including blood and nasopharyngeal secretion, and it is important that the doctor indicates in the request the purpose of carrying out the test so that the sample and reagents used are the most appropriate.

To serve or examine PCR

Or test PCR serve for:

• Investigate virus infectionfungi, bacteria or parasites;
• Identify the presence of genetic alterations which may be indicative of cancer or increase the risk of tumors;
• Monitor the evolution of the disease and response to treatment.

The PCR test aims to promote the expansion of specific areas of the genetic material of people or microorganisms, being useful in diagnosing and monitoring diseases. Therefore, it is important that the doctor indicates the objective of the exam so that the laboratory can use the appropriate and specific reagents for the test.

How is done

The PCR test can be carried out using samples of blood, cerebrospinal fluid (CSF), sputum or oropharyngeal (back of the throat) or nasopharyngeal (back of the nose) secretions.

After collecting the material, the sample is properly stored and sent to the laboratory to be processed and, thus, it is possible to carry out the examination according to the objective.

To take the PCR test, no type of preparation is necessary, however, it is important that the purpose of the test is indicated in the medical request, so that the appropriate material can be collected.

How to understand the result

The result of the PCR test is considered:

• Positive or detectedwhen the presence of a certain region of the gene or genetic material of the infectious agent is identified, for example;
• Negative or not detectedwhen no changes are identified in the samples indicative of mutation or infection, for example.

In some cases, there may also be a value on the exam that indicates the degree to which that change is expressed. In other words, in the case of virus infection, the number of copies of the virus identified in the sample can be indicated, so that the greater the number of copies, the greater the risk of the infection being serious.

In the case of investigating mutations, for example, the value indicated in the test indicates the risk that that mutation could lead to a disease, and it is important that it be evaluated by the doctor.

RT-PCR para COVID-19

RT-PCR for COVID-19 aims to confirm or rule out infection with SARS-CoV-2, which is the virus responsible for the disease. Therefore, this test is indicated in the following situations:

• Presence of suspected symptoms of COVID-19especially 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 resulteven in people without symptoms;
• Recent close contact with infected people by COVID-19, even without symptoms.

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