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In times of pandemic, various scientific concepts have taken over the pages of portals and newspapers, radio and television minutes. We have already become familiar with the “PCR” when hearing about a Covid-19 positive patient, but a few days ago a new test was added, which for now is being applied to Health officials in our country: it’s about antibodies or colloquially called “quick test”.
Sars-Cov-2 is a type of coronavirus. It is basically made up of genetic material (RNA) wrapped in a layer of lipids (fat) and proteins.
The test of PCR it is a “polymerase chain reaction” and measures the presence of genetic material of the coronavirus in a sample obtained from the mucous membrane of the patient. Its results take several hours and certifies that a person is infected.
It is a complex process, which requires qualified personnel in a certified laboratory, but put simply: if RNA appears in the sample, the patient is positive; and if not, it is negative.
It must be considered that in the face of a viral disease, such as that caused by the coronavirus, the human body generates antibodies.
An antibody “is a protein that is produced by the immune system, which is highly specific, and which is created to chemically mark the virus” and thus attack the invader, says Rodolfo Valenzuela, an academic internist at the University’s School of Medicine. Finis Terrae and deputy medical director of the Vespucio Clinic.
They are like an army of defense. The first, and fastest acting, response group is the type M immunoglobulin (IgM). This type of antibody will work and be removed until there is a sufficient amount of type G immunoglobulin (IgG), which “is memory” and has the ability to provide an immune response.
The antibody test measures the presence of IgM and IgG in a blood sample. Its results take minutes (that’s why it is called a rapid test) and it allows us to establish that this person – at some point – contracted the virus and at what stage of the disease is it.
In this type of measurement, bar C is for control, that is, it must be marked to validate that the test is good, the second is G and marks IgG, and the third is M, marking IgM.
If you check only C, it is negative.
If you mark C and G, it is positive for IgG.
If you check C and M, it is positive for IgM.
If you check C, G and M, it is positive for both.
Generally speaking, if only IgM is positive, it can be inferred that the patient was recently infected and recovery is beginning; if it tests positive both, it is that it is in a middle stage of the disease; while if you test positive for IgG only, you are in the final stages of illness or recovery.
Valenzuela mentions that the potential usefulness of these tests lies in the fact that they would help to get out of the diagnostic uncertainty, but warns that if the results give a weak reagent, it must be confirmed with PCR, because it could mark a false positive.
As this graph shows, it can be seen that during the progression of the blue curve the patient should test positive for the PCR, while when the antibodies appear (green and red) they will test positive for one or both, depending on the stage in which is found.
The scientific question today is how long the presence of IgG in the blood lasts and if it guarantees that the patient will not get sick again, so immunity not yet possible to the Sars-CoV-2 virus.
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