The slogan before sitting at the table with parents, grandparents and other families should be clear: avoid infections. For this, all the precautions are few and taking a previous test will be of great help. But which of the different types of coronavirus detection tests provides us with the maximum security?
With the Christmas celebrations just around the corner, worry and doubt are mounting. We refuse to give up meeting with at least the members of our closest family, we want to toast with friends that we have not seen for a long time … and yet, we must not lose sight of the fact that each of the dinners and meals that we celebrate involve a risk of contagion.
In any home in which people other than the usual cohabitants gather, there is the possibility of starting an outbreak of infections that, together with others, would lead us to the dreaded third wave of the pandemic. Therefore, previously knowing our current situation through a diagnostic test helps to minimize risks, although we must never lower our guard or dispense with the basic preventive measures that we already know: limit the number of people as much as possible, wear masks and remove them only at the time of taking a bite, ventilate the rooms, maintain the distance even if that means giving up the hugs that we have so much desire to give …
What tests are there and which is the most appropriate for Christmas?
It is the reference technique for the diagnosis of the SARS-CoV-2 virus in the early stages of the disease since it is a very sensitive system, being able to detect very low amounts of virus. “If the test is positive (it detects viral RNA) we understand that there is viral multiplication. This test us confirms the existence of an active infection and that the individual is capable of infecting others. Until the CRP is negative, the individual is considered potentially contagious ”, explains the Dr. Daniel Carnevali, head of the Internal Medicine service of the Quirónsalud Madrid University Hospital.
Therefore, this test informs us if we are currently infected and if we are therefore contagious (whether or not we have symptoms). If the presence of virus is detected in the nasopharyngeal mucosa, the patient can spread it to the people in front of him through coughing or microdroplets of saliva.
Some Quirónsalud centers have incorporated the most advanced technology to speed up the results of these tests. This is the case of the Quirónsalud Torrevieja, Alicante and Murcia hospitals, among others, which have a new technique in their laboratories for performing up to 1,000 daily PCR tests and obtaining results in less than 24 hours, which allows maximum adjustment of the results in the pre-Christmas dates for maximum security. “This new equipment allows us to be faster and more efficient during the RNA extraction and purification procedure in samples from patients with possible Covid-19 infection. Therefore, these advantages translate into a shorter response time in obtaining PCR results. Furthermore, as it is an automated process, manual errors in the technique and possible cross-contamination between samples are minimized “, explains the doctor. Juan José Mata, specialist in the immunology laboratory of the Quirónsalud Torrevieja hospital and in Quirónsalud Alicante.
“Rapid PCR, not to be confused with antigen tests, combine the advantages of both tests. On the one hand, the speed of the result, similar to antigen tests and, on the other, the reliability in the diagnosis provided by a PCR ”, adds the Dra. Elena Llompart, head of the Laboratory of Clinical Analysis of Rotger Clinic and Hospital Quirónsalud Palmaplanas. In short, this test, if it is carried out a few hours before the Christmas celebration that we have planned, is the one that can give us the greatest security.
* The advice. This test offers us all the reliability of our situation at the time of carrying it out, so the ideal for maximum security is to keep isolated, have minimal social contact and avoid contagion situations from the moment we perform the test until we sit down at the table with our relatives.
If a negative result is obtained from a patient with a high suspicion of infection with the SARS-CoV-2 virus, it should be confirmed with a new test.
PCR in saliva
It is a novel PCR modality that allows detecting coronavirus infection through saliva. Until now, PCR consisted in the introduction of the swab in the nostril and throat, being a very annoying technique, so the main advantage of this new variant is that the procedure for extracting the sample in saliva is much simpler and more comfortable if We compare it with the rest of the tests that we can currently perform.
The ‘dreaded’ nasopharyngeal swabs are no longer necessary, which are so annoying for patients and which are mandatory both in performing PCR and for antigen testing. In the PCR in saliva it will be enough to deposit saliva in a bottle or chew a ‘salivette’ (cotton swab similar to the one used by dentists to absorb excess salivation). “This brings many significant differences, such as the fact that the test becomes very little hassle and the ease of obtaining the patient sample. This facilitates the work ratio and the risk for the person who obtains it. The salivary sample will also be treated using the PCR technique, so the efficiency continues to be extremely high in detecting the Covid virus ”, explains the Dr. Jordi Robert, Head of Section of the Internal Medicine Service of the Dexeus University Hospital. Once the sample is obtained, it is processed in the laboratory exactly like any other PCR and the result is obtained with the same reliability.
* The advice. By eliminating rods from the equation, this non-invasive test is especially suitable for children and the elderly. Of course, before taking it, a series of measures must be taken, such as not eating, drinking, chewing gum or smoking during the 30 minutes prior to taking the sample and, preferably, doing it first thing in the morning, without having applied makeup, cream or lipstick.
They are performed through a nasopharyngeal sample and are capable of diagnosing the SARS-CoV-2 virus from the onset of infection and with the same reliability as PCR, with the advantage that you can have the results in 15 minutes. This allows greater agility in decision-making both individually and in a group. He Dr. Luis Manuel Barrena Santana, from the Internal Medicine Service of the Quirónsalud Clideba Hospital points out that “the new antigen tests look for the protein directly, it is a faster system because it avoids many laboratory procedures. From the moment the patient enters, in half an hour we can have the result, which is an important advantage from the point of view of decision-making and patient control. It is applied to patients with symptoms and represents a before and after in decision-making. Furthermore, it is important to emphasize the importance of these tests always being carried out according to medical criteria ”.
* The advice. This test is recommended for patients with symptoms, since thanks to its quick results it allows to take isolation measures in an early way. It has a sensitivity of 100% if the sample is taken until the third day after infection. In the case of symptomatic patients with 5 days or less, it has a sensitivity (ability to detect the disease) of 98.2% and a specificity (the ability to detect real negatives) of 99% and with 7 or fewer days, the sensitivity varies to 93.3%. The sensitivity in asymptomatic patients is also high, which is an asset in favor of preventing the spread of the virus.
They are effective in determining our immune status, but they do not measure the presence of the virus at the moment. This test, which is done through a blood sample, detects and quantifies the antibodies that our body has generated against the virus. Our immune system has a way of detecting external agents which is the generation of antibodies called immunoglobulins (Ig). These immunoglobulins are proteins that recognize, capture and block viruses so that the cells of the immune system (lymphocytes) can recognize and eliminate them.
Although there are up to five types of immunoglobulins, in case of infection we are interested in IgM (the first to appear) and IgM (which appear in a more advanced phase of the infection) because they offer very valuable information on what phase of the infection is in the patient. “Immunoglobulins do not determine the presence of the virus, but rather the immune response of our body when we have been exposed to the virus; that is, if the individual has been in contact with the virus, whether or not they have developed symptoms “, clarifies the Dr. Daniel Carnevali, head of the Internal Medicine service of the Quirónsalud Madrid University Hospital.
If when carrying out an antibody test only the presence of IgM is observed, we are probably in the initial stages of the infection. When the analysis shows IgG and IgM, we think that more time has passed since the beginning of the infection and that there are remains of the acute phase. When only IgG antibodies are observed, we think that the viral replication phase has passed.
In summary: “Serology gives us great information about the moment in which the infection is found –Explains the Dr. Miguel Marcos, Head of Internal Medicine at Quirónsalud Málaga–. A few days after infection, an antibody, IgM, becomes positive, which tells us of a current or very recent infection, remaining positive until approximately 21 days. If the result is positive IgG, it tells us of an infection that has progressed beyond day 14 and remains positive for an undetermined period of time, so it could tell us about a past infection. And probably, it will also inform us of our immunity to infection based on having previously presented it “.
* The advice. These tests establish the immune status but not the presence of the virus at the present time or the possibilities of being contagious. Therefore, in cases in which there are no symptoms, if you want to be absolutely certain that they do not suffer from or transmit COVID19 (because they are contacts of high-risk people, for example) it is recommended to perform a serology first and, if we obtain a positive IgM result, the diagnosis should be complemented with a PCR test.
Advanced technology to differentiate covid-19 from other respiratory diseases
Along with all this diagnostic arsenal, the laboratories of the Quirónsalud hospitals managed by its company Health Diagnostics have the latest rapid molecular syndromic diagnosis technology, capable of detecting not only SARS-CoV-2 but also twenty more possible bacteria and respiratory viruses.
In addition, to help in the crisis of patients with Covid-19 they also use the so-called Pneumonia Panels, capable of detecting superinfection in the most serious patients admitted to the ICU. These tools allow a total of 27 respiratory pathogens and 7 antibiotic resistance genes to be diagnosed in approximately one hour, facilitating the adequate adaptation of antibiotic treatment and reducing the proliferation of multi-resistant bacteria.
“Thanks to these syndromic technologies, we have managed to diagnose the most serious patients for these pathologies in approximately one hour, achieving an accurate diagnosis in a clinically relevant time that allows adapting the therapeutic aptitude and patient management”, has pointed out Dr. Miguel Ochando, corporate director of Health Diagnostic laboratories.
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