Antigen tests to detect a Covid-19 infection are already part of everyday life in society. The price of tests in private clinics or the two days of waiting that a PCR entails have driven the commercialization of these rapid tests, which is why hundreds of Spaniards resort to this test.
However, the fact that its use has spread does not imply that its reliability is the same as that of a PCR. In fact, antigen tests were only 58% accurate for people without symptoms, or 72% accurate for those with symptoms, according to a Cochrane review of more than 24,000 samples. In addition, these data correspond to the period prior to the discovery of the Omicron variant, so the ability of this test to detect it is currently unknown.
In contrast, despite the difference in waiting time, a PCR obtains drastically more reliable results, reaching an accuracy of 98%.
However, with the arrival of the Christmas holidays, many people will be in contact with their older relatives and, therefore, with a population at high risk of contagion, so many will be forced to resort to these tests, regardless of its reliability. For this reason, it is vital to pay attention to the four factors that can falsify the results of an antigen test purchased in a pharmacy, according to Insider.
The tests have an expiration date
Fearing a possible shortage, many people purchased a large number of tests months ago. However, these tests have an expiration date, so they cannot be used if it has been exceeded.
These kits between 6 and 14 euros usually indicate on the box itself both the date of manufacture and the expiration date, so the user can find them at a glance, it is always convenient to check this information before proceeding to use it.
It should be noted that the expiration date of most of these tests usually ranges between four and six months. Anyone who takes an expired test must assume that the result will be wrong.
Temperature affects the result
Both the temperature at which the test is stored and the one at which it is performed will alter the test result, since the liquid that must be mixed with the extracted sample is extremely delicate and extreme temperatures can corrupt it.
“Don’t do rapid tests when it’s really cold, that can decrease their effectiveness,” said Michael Mina, chief scientific officer of eMed, one of the companies that makes these kits. “You should do it at room temperature as much as possible.”
These temperatures vary between manufacturers, so, in the same way as with the expiration date, the temperature at which it should be stored will be indicated on the box itself or on the leaflet. As a general rule, these kits should be stored between 2 and 30 degrees, although for their use it must be ensured that all the components are at a medium temperature.
Food and drink disrupt the test
At the moment, in Spain, there is only one authorized test that is carried out orally and not nasally: COVID-19 Antigen Rapid Test / Hangzhou Alltest biotech Co. However, these may increase in the near future, so It should be noted that the food or drinks ingested will also affect the test.
Products such as coffee, fruit juices or any acidic food or drink compromise the integrity of the test. However, at least these types of products, including Coca-Cola, cause a false positive, rather than failing to identify the infection.
On the other hand, experts also do not recommend brushing your teeth or rinsing with mouthwashes. Users must not perform these acts, as well as they must neither eat nor drink, during the 30 minutes prior to the test, at least.
It is unknown if they detect Omicron
At the moment, it is too early for the health science community to know the ability of these tests to detect the Omicron variant, so in many cases an infected person could give a negative result.
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