We tend to hear about COVID-19 tests as if it were only one, but the truth is that there are different tests designed primarily to detect a current or past infection of SARS-CoV-2 , the virus that causes COVID- 19.
It is true that the different tests that exist so far can be confusing. And sometimes it is not entirely clear why they are being carried out, what the implications and limitations of their results really are.
In general, COVID-19 tests are fundamentally divided into a total of three main categories: CRP, antigen, and antibodies. As thousands of tests are carried out in our country every day, it is convenient to strengthen the understanding about these tests.
What is a PCR?
A polymerase chain reaction (PCR) is a laboratory technique used to detect small amounts of genetic material in a sample (in this case, RNA from the SARS-CoV-2 coronavirus). Thus, if there is a sufficient amount of viral genetic material within the individual’s sample, which can be amplified above a certain level, that person is considered to be “positive” for said virus.
Ultimately, the PCR test is useful to indicate to the specialist if the person in question has the infection at the time the sample was taken . It has a high rate of precision when carried out by trained professionals. Furthermore, it is a very sensitive test, capable of detecting very low levels of genetic material in a sample.
However, it is important that the throat and nose swabs are carried out correctly, and at the appropriate time after infection, in order to ensure that there is enough virus in the sample obtained from the patient.
How does a PCR test work and how is it done?
The PCR test requires that a tissue sample be taken from the patient’s nose and / or throat with the help of a swab, which is covered with an absorbent material. The swab is then swirled for about 15 seconds, then carefully removed.
Finally, the sample obtained is sent to a laboratory for analysis. It is important that the sample is collected about a week after the person has been infected, even if they have no symptoms (that is, they are asymptomatic).
We must bear in mind that the samples are only useful when the coronavirus infection is active . Therefore, once the infection is gone, the test will not be helpful and will not indicate whether the person has been previously infected or not, because the viral genetic material is no longer present in the body.
How to understand PCR test results
It is, as we have indicated, a very sensitive test, but it is very important that it is carried out correctly in order to guarantee that there is a sufficient amount of virus in the swab. But, as with all medical tests, they are not perfect.
So far, studies have suggested that up to 30 percent of results are inaccurate, while with COVID-19 tests, false negatives appear to be significantly more common than false positives (ranging from 2 to 37 percent). Therefore, if you get a positive result, it is very likely that you have the virus.
For example, a false negative could occur if the healthcare professional taking and collecting the sample does not go deep enough down the throat or nose that they will not collect a good sample. In addition, the moment in which it is carried out is equally important . Infections could be missed if the test in question is carried out too soon after exposure, as research published in June this year showed.
But the opposite could also happen. In other words, sometimes once the virus has been eliminated, there may still be a lot of genetic material in the body. This could cause a person to test positive even when they are not actively sick. Thus, according to experts, getting tested around five days after a possible exposure seems to be the best time .
Can a CRP hurt?
Since we are not used to having any object placed inside the nose, it is common for many people to feel uncomfortable at the time of this test.
It is possible to experience several different sensations during the PCR test for COVID-19. For example, those who have done it report deep burning inside the nose, transient pain, sneezing, coughing, and gagging (when the swab comes into contact with the back of the throat).
The test can be even more difficult when your nasal passages are blocked as a result of an allergy, or symptoms similar to those of the common cold or nasal polyps.
In any case, it is generally a painless test in most cases, essential when it comes to detecting possible positive or negative cases of COVID-19.
