PHOENIX, Ariz .– As the coronavirus spreads more in the community, the demand for the tests and tools available to detect the infection increases. There are currently three types of tests: the PCR or molecular test, the antigen test also known as the rapid test, and the antibody test.
“The antibody test is a blood test and indicates if you already have an immune response to the coronavirus, if your body already recognizes it as an invader”, says Dr. Pedro Rodríguez.
“The antibody test only says if you have had the virus in the past. It doesn’t say if you are currently infected, ”adds Dr. Joshua Labaer, director of the ASU Biodesign Institute that developed the saliva-based coronavirus test, which is a PCR test.
To detect if you have the virus active in your body, there are two tests: the PCR or molecular, and the antigen also known as the rapid test.
“Rapid tests detect fractions of the virus to tell us if the virus is in you, now the quality of the PCR test that takes 24 and 48 hours to obtain the results, the sensitivity is much higher, that is, it has the ability to capture fragments smaller, bone is a technically better test, ”says Dr. Rodríguez.
Although helpful because of the rapidity of results, Dr. Labaer cautions that you must be aware of the limitations of antigen testing.
“Results are ready in 15 minutes to an hour, but rapid tests are not as accurate if you don’t have symptoms. If you have symptoms, this test may be helpful to you. A study we have carried out indicates that in 70% of the cases of people who do not have symptoms, the antigen test does not capture the virus even though it has it ”, says the director of the ASU Biodesign Institute. “The PCR or molecular test is more sensitive, and is capable of detecting the virus in people with symptoms, but also in people who do not have symptoms and do not know they have the virus.”
“It is very common to do the two tests at the same time, one at the moment to make certain decisions, and the other is already sent while we wait for confirmation,” says Dr. Rodríguez.
To avoid false negatives, the ASU Biodesign Institute recommends that if you have been exposed to a positive person and have no symptoms yet, that you wait five days before having either of the two diagnostic tests.
“If you are exposed to the virus today, and the test is done in three or four days, including the PCR test that is more sensitive, it may be negative, because it takes several days for the virus to incubate, it takes days for it to be detected. in your nose, throat, or saliva. However, on the fifth day it can be positive, ”says Dr. Labaer.
Each test has a different function, and is useful depending on each particular case.
“The best test is the one that your doctor tells you to do, whether in Urgent Care, in primary care, the tests are for you, the patients, to understand what is happening to you, but they are tools for us doctors to know what should we do ”, says Dr. Rodríguez.
Both experts recommend that regardless of the test that is done, even if it turns out negative, people should continue taking all measures to avoid the spread and contagion of the coronavirus because there is always a probability, even with the most accurate tests, of having a false negative.
“We have to tell the community that rapid tests have more than more false negatives, so we cannot say with 100% certainty, I do not have coronavirus. You have to continue taking the social hygiene rules that we have been talking about in these months: wear a mask, maintain social distancing and wash your hands frequently, ”concludes Dr. Rodríguez.