Test for Covid-19: how are they done? Who should test?

The performance of tests to identify people infected with the new Coronavirus is important, as they help to characterize the real situation of a country in the face of the disease, in addition to providing data that allow the isolation of affected patients.

Currently, there are some tests approved in Brazil by the National Health Surveillance Agency (ANVISA).

Keep reading and learn more about them!

What tests for Covid-19 are available?

Currently, there are two main types of tests approved by the National Health Surveillance Agency (ANVISA) to detect infection with the new Coronavirus: the Rapid Tests and the Molecular Examination (RT- PCR ).

They are:

Molecular Examination (RT-PCR)

The molecular exam is currently the most assertive and the one indicated by Anvisa as the best option to make the diagnosis of the disease.

It is done through samples taken from the nose or mouth and allows to identify whether the virus is present in the patient’s body at the time of the exam.

Quick test

Rapid tests are also known as “pharmacy tests” and are performed using a blood sample.

They receive this name, because the exam is carried out and the results are quickly ready, in a period between 15 to 20 minutes.

This type of test allows you to identify whether the patient has already been infected by the virus and his body has developed antibodies. In this way, it does not reveal whether the person has the active virus, it only shows whether he has been infected at some point.

How are they made?

The tests carried out by means of the molecular examination and the rapid test differ from each other in relation to the performance.

Specifically, the forms of application are:

Molecular Examination

In the Molecular Exam (RT-PCR), the test is performed using samples from the nose or mouth. The collection is made with a material similar to a swab (swab) and then sent for analysis in the laboratory.

The result, in general, is ready within approximately 8 to 12 hours. However, with the high demand due to Covid-19, some laboratories may take longer to present the results.

If the answer is positive, it means that the person is infected with the virus and the necessary measures must be taken, such as totally isolating the patient.

Quick test

In rapid tests, the test is done using a small blood sample. The collection is carried out by means of a finger prick and, shortly thereafter, the drop of blood is placed in a test device.

After a period of usually 15 to 20 minutes, the result is displayed.

If the answer is positive, it means that the patient has already had contact with the virus and his body has developed antibodies to fight it.

It is worth mentioning that this test should be done only after the seventh day of the onset of the symptoms of the disease. This is because the test is done based on the presence of antibodies in the body.

Thus, the period between 7 to 10 days is the time necessary for the body to have produced these defense cells, allowing them to appear in the test.

Despite this, in general, Anvisa indicates that rapid tests should not be used as an isolated means of assessing the presence of the disease.

According to the agency, they are only part of the information necessary for the diagnosis or disposal of the pathology. Thus, this examination should be done only by a qualified professional, who will evaluate the results together with information from the patient’s clinical and historical background.

How do the tests work?

The mechanism of operation and presentation of test results varies according to the type of examination performed.

In general, they are:

Molecular examination (RT-PCR)

The RT-PCR molecular exam is done by means of blood samples, so that the analysis can be done in the laboratory.

During the study, the sampling of the patient goes through a series of steps to identify the disease, through the genetic material present in the sample.

This material corresponds to the information that characterizes an individual. They can be DNA – deoxyribonucleic acid – or RNA – ribonucleic acid.

In the case of the coronavirus, its material is RNA. This means that if the patient has the disease, the virus’s RNA will be present in the body, along with human cells. The exam is to identify this.

First, an enzyme called Reverse Transcriptase is added to the patient’s sample.

This enzyme will be activated and, if there is the virus’s RNA in the patient’s sample, it will transform it into DNA.

From that moment on, the DNA cell is enlarged and professionals check whether there is a gene – responsible for the inherited characteristics of an organism – that corresponds to the virus gene.

In a simplified way, the steps are:

  1. Collect the sample;
  2. With an enzyme, transform RNA into DNA;
  3. Amplify the DNA;
  4. Check if there is a similarity with the genes of the new Coronavirus;
  5. Issue the result.

If the result is positive, confirmation is made and the person is infected.

In general, at that moment, preventive measures are taken, such as totally isolating the patient and even hospitalization, varying according to the clinical condition.

Quick test

Rapid tests are performed by means of serology, that is, the identification of antibodies – the body’s defense element – in the body, by means of blood samples.

The methodology used to perform this exam is called immunochromatography.

This feature makes it possible to make the presence of antibodies in the body visible, in addition to, if the result is positive, indicate whether the patient’s contact was recent or not.

This is done by means of a chemical reaction between antigen (substance foreign to the body) and antibody.

After the reaction, a stain is generated under the surface on which the test was performed, which indicates the result, as in a pregnancy test.

In the case of Covid-19, the results obtained are of two types: IgM and IgG. Both are defense cells of the organism to external agents.

IgM is a marker of the acute phase of the disease, that is, it demonstrates that antibodies started to be produced recently, 5 or 7 days after infection.

IgG, on the other hand, indicates the antibodies that remain circulating in the body even after the acute phase, which indicates that the patient is, theoretically, protected against new infections – however, it is highlighted that there is still little information about the immunization of the coronavirus . In other words, there is no guarantee that anyone who has already caught the disease cannot be infected again.

Possible responses to the test can be:

IgM IG G Result
There was no contact with the new Coronavirus.
+ Recent infection with the new Coronavirus has been identified .
+ Old infection identified by the new Coronavirus, with the presence of antibodies to fight the disease.
+ + Recent infection identified with onset of antibody production .

For positive results of recent infection , it is recommended to perform the test again after a period of 14 days, in addition to following the recommendations of the World Health Organization (WHO) and the Ministry of Health.

Who should be tested for Coronavirus?

Ideally, all people who show symptoms for the disease should be tested.

However, until then, the tests were being carried out preferably on hospitalized patients and health professionals. In addition, a medical indication was necessary to perform the test.

This, due to the limitation in the number of testing kits available in Brazil.

However, last Wednesday (6), the Ministry of Health released a new strategy for conducting tests in the country.

It is the program called “ Diagnose to Take Care ” and aims to carry out tests on a large scale. It is divided into two fronts, “Confirma COVID-19” and “Testa Brasil”.

The first, Confirma COVID-19 , consists of applying RT-PCR tests to people with mild, moderate or severe symptoms and will be done within 7 days after the onset of signs of the disease.

The second, Testa Brasil , will be done by means of rapid tests, applied from the eighth day of symptom onset, in people who show signs of the disease.

Asymptomatic people, that is, those who do not have any symptoms, should participate in research through interviews, such as those carried out by the Brazilian Institute of Geography and Statistics (IBGE).

In general, the objective is that the people who participate in the research, in addition to providing data about the virus in the country, are also tested through rapid tests.

Are pharmacy tests safe?

On the last 28th, Anvisa temporarily released tests in some Brazilian pharmacies. The exams done are called rapid tests.

In general, they are not completely safe, so they should not be used as the sole means of diagnosing the disease.

This, due to the possibility of false negatives, that is, errors in the result.

The rapid tests aim to identify the presence of antibodies against Covid-19 in the patient’s body.

In general, when a pathology is installed in the human body, there is a period of “immunological window”, that is, the time that the organism takes to produce these defense cells.

In the case of the new Coronavirus, if these tests are performed at the beginning of the infection, that is, within that period of immunological window, there has not yet been enough time for the body to react and develop antibodies.

Thus, the result can be negative, even if the person has the virus.

Therefore, tests should be performed only by qualified professionals, and the interpretation of the result made according to the patient’s clinical condition, taking into account their history and symptoms.

When can I get a quick coronavirus test?

For rapid tests, the application can be made from the seventh day onset of symptoms.

However, the ideal is that it is carried out from the tenth day, so that the result is more accurate. This, in order to avoid that the exam is done within the immunological window and there are flaws in the result, such as false negatives.


Testing for Covid-19, both in people who have symptoms and in asymptomatic people, is important to provide data and help control the spread of the virus.

Thus, it is worth understanding the functioning of each type of test that is being or will be applied to the population, so that there are no doubts.

Want to read more about the new Coronavirus and health ? The Healthy Minute has other complete content for you! Read more and stay informed!

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