How The Test To Detect The Coronavirus Works We remain on alert and although the population is confined, the virus continues to spread. How do we know? That is, how do we know for sure that someone is infected? Are there false positives? And negatives?
Doubts about the functioning of the diagnosis, as is logical, arise among the population. We will explain the most common method of detecting the disease, how it works and what errors it can make, because information is power.
When a person shows symptoms and offers suspicions of coronavirus infection, automatically, in Spain, they are placed in voluntary or hospital preventive isolation, depending on the situation. The case is immediately confirmed. The first way to do it is through the symptoms and the clinical picture. Molecular techniques are also used to overcome doubts.
The standard technique is to perform a PCR. By these abbreviations, “Polymerase Chain Reaction”, we refer to a procedure that consists of the following: a sample of secretion is taken, usually mucus or saliva, where the virus can be found in case of infection. This sample is taken to the laboratory and processed with a series of special substances.
The virus contains within it a chain of RNA with the information it needs to reproduce. What these substances do is release this chain. Then, the PCR process takes this chain and, by means of the polymerase that bears its name, reproduces this chain, copying it and multiplying it by millions.
Why You Should Forget Everything You Learned About This Is How The Test To Detect The Coronavirus Works
Why do we want so many copies of the virus RNA? Very simple: what we do next is to use a molecule with a colored or fluorescent substance that sticks to the RNA strand. If we only had a few (thousands, for example) it would be very difficult to detect it. However, having billions or billions of molecules we can see more clearly these molecules that signal the presence of RNA and, therefore, the virus. The process is more complex and has several variants, but the basic concept is enough to understand how it is done.
It is very difficult for this false positive procedure. For this to happen, the sample would have had to be contaminated with virus RNA, exclusively. This, as you will understand, is almost impossible if the appropriate control measures and protocols are carried out. In the case of COVID-19, these protocols are carried with extreme care.
In any case, a false positive, although it is counterproductive since it involves taking drastic measures against a threat that is not, is not as dangerous as a false negative, which would prevent the detection of an infected person. In fact, some false negatives are known. As the scientific journalist Angela Bernardo explained, speaking about the Díaz Ayuso case, this can happen due to several reasons:
Temporary asymptomatic cases: the virus has not yet shown its face and may be in low concentrations in our body. You could go unnoticed by this test. Poor sample collection: As some studies show, poor sample collection can end in a false negative.
Poor extraction of the sample: as we said, in the PCR test it is necessary to obtain the RNA of the virus applying a certain prior technique to the copies. If it does not work and the RNA is not extracted or destroyed in the process, it could give a false negative. As we said, this is infinitely more dangerous than a false positive since it leaves a vector (a person who can transmit the virus) with a false sense of security, and can become a much more serious source of infection.
Yes. Right now, the first immunological (rather than immune) kits for virus detection are emerging. These work in a similar way to PCR in that a substance is used to “color” the presence of the virus. However, it is not necessary to multiply the RNA chains because this time, what is used are antibodies that directly detect the virus and its parts.
In this way, these antibodies, as they would do in our body, stick and, in turn, allow us to point out where the viruses are, as if it were a beacon. These kits are faster than PCR since they can be performed on the spot and with a sample of fluids directly.
On the other hand, they are also less sensitive than PCR and are also equally sensitive to false positives. In any case, both one system and the other, although relatively cheap, have a cost. What is clear is that with the advent of immunology kits, diagnoses could be facilitated and accelerated, if they are adopted more commonly.