Peru: When must antigen COVID tests be conducted?

Photo: ANDINA/Ministry of Health of Peru

Photo: ANDINA/Ministry of Health of Peru

12:16 | Lima, Mar. 2.

If you have a family member showing any symptoms and is suspected of being infected with coronavirus, but you do not know what type of test he/she should undergo to confirm or rule out the infection or what type of measures to take to protect other family members, here we tell you how to proceed.

In remarks to Andina news agency, Dr. Lely Solari —infectious disease physician at the National Health Institute (INS)— commented that the first thing to do in the face of coronavirus suspicion is to assume that every person in that household is COVID-positive.

"Once COVID-19 enters a family, the contagion rate is quite high. So, it is better to assume that everyone is positive, abide by social isolation, follow sanitary measures (wearing a face mask at home, plus washing hands constantly), and monitor the health status of every member (under medical supervision)," she indicated.

If despite everything, the family insists on subjecting the suspect to a test, the ideal would be the antigen test since it is basically designed for COVID-19 patients with symptoms, said the INS expert.

Instead, if the person does not have any coronavirus symptoms and the antigen test is conducted, there are few chances that the result will be valid because "the detection power of this test is lower when there is few virus in respiratory secretions." 

According to the Health Ministry (Minsa), rapid diagnostic tests based on antigens detect the virus. However, they do not look for genetic material but rather identify the proteins found in its external part.

In this case, the sample is taken by means of a nasopharyngeal swabbing, and the result is obtained in less than half an hour, since it does not require a laboratory for processing.

Antigen tests cost less, are used for diagnosis, but must also be conducted during the first days of the disease.

Types of test

It must be noted that there are three different tests which allow people to know if a person is infected with COVID-19: molecular, antigen, and serological tests.

Molecular (considered the golden tests by the World Health Organization) and antigen tests are diagnostic tests, whereas serological tests (rapid tests) are antibody tests.

These tests detect the genetic material of the virus (RNA); that means the virus itself, in nasal mucosa or saliva samples during the first seven days of infection.

After the first week, the virus amount decreases and the molecular test is no longer effective at that time. Results can take between 6 and 8 hours.

Rapid tests

According to Dr. Solari, serological or rapid tests (which measure the antibodies that appear when the body attempts to defend itself from infection) are now not as useful as they had been during the first coronavirus wave.

"What happens is that more than 40% of the population has already been infected, and even more so during the second wave (...). Measuring antibodies now is not useful as it was during the first weeks of the pandemic (…)," she said.

The expert recalled that rapid tests "were used a lot" during the first phase of the pandemic because there was only one laboratory available for the whole country, meaning that run by the INS.

However, every region currently relies on a molecular biology laboratory. In addition, antigenic and molecular tests are more available than before, she concluded.


Publicado: 2/3/2021