Explanation of the Different Tests for COVID-19

There is a lot of talk about tests for COVID-19, and there is also a lot of confusion about what the results might mean. If the test result for COVID-19 is negative, does this mean that he is not sick? If someone tests positive for antibodies against COVID-19, does that mean they are immune?

Currently, there are two main types of tests for COVID-19: diagnostic and serological. A diagnostic test works by looking for the genetic material of a virus that can be detected during an active infection. A serological test works by detecting antibodies against the virus, which are only found later during infection and also after you have recovered.

“Each test has its own strengths and weaknesses,” said Pedro Piedra, MD , professor of molecular virology, microbiology and pediatrics at Baylor College of Medicine.

Diagnostic tests look for a virus

If you’ve heard of a test in which a swab is stuck in your nose and held all the way to your back , this is a diagnostic test that works by looking for the virus itself. A number of diagnostic tests have been developed, each of which works by looking for the genetic material of the virus.

A positive result means that the patient has been diagnosed with a virus, which indicates an active infection. Viral particles are found in a patient when they show symptoms and for a short period before and after, during the so-called spread of the virus.

But if you’ve been tested for COVID-19 and tested negative, that doesn’t necessarily mean you’re not infected.

“The main problem is often poor quality samples,” said Piedra. It is difficult to obtain a sufficient amount of sample, especially under imperfect conditions. He also advises that you discuss the test results and their significance with your doctor.

Serologic tests look for antibodies against the virus

Serological testing has received a lot of attention lately, mainly because it is spoken of as a measure to revitalize society by identifying people immune to COVID-19. Serologic tests work by detecting antibodies against the virus that causes COVID-19. These antibodies indicate that a person has been exposed in the past, whether they become ill or not.

There are two types of serological tests, one that checks for IgG antibodies and the other for IgM antibodies. IgM antibodies are the first line of defense of your immune system and are produced earlier in the course of infection. IgG antibodies take time to build up and can be detected in the body after the infection has passed.

A negative serological test does not necessarily mean that you are not infected.

“Both types of antibodies take time to create, so in an acute setting you won’t be able to detect them and you will have a false sense of security,” says Louis Ostroski , MD, an infectious disease specialist at UTHealth’s McGovern School of Medicine. in Houston.

Serologic tests are possible indications of immunity

The big conversation around serological testing is that a person who tests positive is immune to COVID-19. In theory, this would mean that a healthcare professional could safely care for COVID-19 patients, key workers could be allowed to return to work, and others could be released from quarantine or isolation.

As hopeful as this idea sounds, things might not be that simple. “There is still a lot we don’t know,” says Piedra. Some of the unknowns include whether a person could be re-infected with COVID-19, and how long that immunity lasts.

If your antibody test comes back positive, don’t assume that it means you can return to your normal life. “You should still talk to your doctor,” says Ostroski.

Why is it important to confirm COVID-19 infection?

Testing for both varieties is still lacking, which means there are people with symptoms similar to COVID-19 who have not been able to get an official diagnosis. Even in these situations, Ostroski and Piedra are adamant: it is important to confirm that this is indeed COVID-19 before making any assumptions. If you have had symptoms of COVID-19, but you have not had an official diagnosis, this does not mean that you are now immune.

“It is very important to know for sure whether you have had the disease or not, as it can give you a false sense of security and put you at risk of infection,” says Ostroski, while Piedra notes that there are many respiratory viruses that mimic the lungs. or mild symptoms of COVID-19.

If you have had symptoms of COVID-19 but have not had an official diagnosis, that does not mean that you are now immune, and that does not mean that you can stop measures such as hand washing and physical distancing.

“Don’t be on the alert just because you think you have been infected,” says Piedra.

In the meantime, we must all do our part to flatten the curve to help protect the safety of healthcare workers as well as the health of our community. So wash your hands, practice physical distancing, and stay home.

“We’re in this for a long time,” says Piedra.


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