So are the PCR tests used to detect the coronavirus

The technique used to detect the coronavirus is the PCR, for the acronym in English of "polymerase chain reaction", and is not new.It was designed by the eccentric Nobdle.

PCRs are used every day in thousands of laboratories around the world to determine paternities, identify corpses and detect diseases;In this case, to diagnose SARS-COV-2 infection, the virus caused by COVID-19.

This infographic made by Compound Interest and translated into Spanish by Claudia Blanco and Fernando Gomollón summarizes the entire PCR detection process, explains its limitations and describes what future tests will be like.

As explained on the compound interest website, the tests for the virus need a sample, which is collected from the nose or the back of the patient's throat.This material is placed in a safe container and sent to a laboratory for analysis.

The process, step by step

DNA constitutes our genetic material, but Sars-Cov-2 does not contain double chain DNA, but RNA, of a single chain.As PCR tests can only make DNA copies, you must first convert RNA into DNA.

PCRs are used every day in thousands of laboratories around the world to determine paternities, identify corpses and detect diseases

The RNA of the virus extracted from the sample is purified and mixed with an enzyme called reverse transcriptase, which converts the single chain RNA into double chain DNA.The viral DNA is added to a test tube together with primers - short DNA sections designed to join the virus - nucleotides - the construction blocks that make up the DNA - and an enzyme construction of DNA.

The PCR machine heats the mixture.This causes double chain DNA to be unleashed and the primer can join the DNA as it cools, providing a starting point for the DNA construction enzyme to copy it.This process continues through repeated heating and cooling until millions of Copies of DNA have been created.

This explains how the PCR amplifies the genetic code of the virus, but not how it is detected.This is where fluorescent dyes enter, added to the test tube while the DNA is copied.They bind to the copied DNA, which increases their fluorescence causing them to emit more light, which allows the presence of the virus to be confirmed.

Fluorescence increases as more copies occur and, if a certain threshold crosses, the test is positive.If the virus was not present in the sample, the PCR test will not have made copies, so the fluorescence threshold will not be reached and, in that case, the test will be negative.

The limitations

PCR tests are a fairly reliable way to verify the existence of infectious diseases, however, they also have limitations.

The first is that they have been.A few hours are needed to get results.This implies a limit on the amount of tests that a single laboratory can carry out in one day.

The PCRs have been implying a limit on the amount of tests that a single laboratory can carry out in one day

Another limitation is the availability of necessary reagents.The world demand for these tests following the pandemic has caused shortage.

Contamination or degradation can also cause problems due to false positives (when someone does not have the virus but the test says it does) or false negatives (when someone has the virus but the test says it does not have it).

A last great limitation of this type of test is that they can only indicate if someone has the virus at the time of the test.You cannot tell us if it has had the virus but has been recovered later before the test.

Another type of test: the antibody

Antibody tests serve to know if a person has immunized after being infected

Antibody detection tests are much faster, only 15 minutes are taken to have the result;And the sample is obtained from a drop of blood extracted from the finger.The Ministry of Health has announced the distribution of 650.000 test of this type and more units imported from Europe are expected.

These antibody -based tests serve if a person has immunized after being infected.That is, it detects the antibodies generated by the immune system of our body when the infection has already passed or we are recovering.

Normally it is recommended to use them complementary to the PCR, but in situations like this, in which the massive distribution of tests is necessary, they will be of great help to detect cases of infected people who do not have symptoms or suffer them in a very slight way.