5 things you should know about antigen tests
False negatives? False positives? How effective are antigen tests? Do they detect the Omicron variable? Below we resolve the main doubts about antigen tests.
Over the past Christmas, antigen tests have been the star test on which a large part of the population has relied to find out if they are a carrier of the SARS-cov-2 virus, the virus that causes Covid-19, and how. no, to decide whether or not to get together with their loved ones.
This diagnostic test has unbeatable characteristics compared to others: we do not need training, we have the results almost instantly and, in addition, they are low cost. That is why these tests have been used as a form of screening for the possible involvement of the virus, and are used to decide if a patient should undergo a PCR. However, they are not always infallible: while they are very reliable in the case of positive results, they can give false negatives.
That's why we tell you 5 things you should know about antigen tests
How effective are antigen tests?
According to studies published by the scientific journal Clinical Epidemiology Journal , antigen tests are 80% effective in detecting any level of Covid-19 infection during the first week of infection. They are effective even when the patient has no symptoms, so these tests have been shown to be particularly effective in detecting asymptomatic patients.
For people who have developed symptoms, the effectiveness of these tests rises above 90%.
Therefore, we can say that yes, antigen tests are today the fastest, most effective and easiest way to detect if we are infected by the Covid-19 virus.
What happens if I have symptoms compatible with the Covid-19 virus, but the antigen test gives me a negative result?
In case of having symptoms compatible with the Covid-19 virus, such as fever , respiratory problems , loss of smell... the conclusive test of whether or not we are infected is the PCR. Therefore, we must notify our health center that we have compatible symptoms and they will tell us when and how to do the PCR. It is possible that, in case of doing an antigen test, it could be negative and make us believe that we are not infected. In these circumstances, it is advisable to take extreme precautions and not trust a negative result in an antigen test.
It must be remembered that the conclusive test is the PCR, so to avoid a "false negative", we must undergo a PCR. In this way, we will avoid putting third parties at risk.
Are there false positives?
Although a positive result in an antigen test is 90% plausible, it is not always accurate, and it should be noted that it can also give “false positives”. This happens when the antibody detects the virus genome, but it is incomplete. This means that although the antigen test has detected the virus, it may no longer be active. In any case, whenever the result of the antigen test is positive, it must be contrasted with a PCR test. While both antigen and PCR tests have similar reliability for positive results, PCR tests have higher reliability for negative results, so PCR can detect those “false positives” obtained in antigen tests.
Are Omicron variant antigen tests effective?
The study carried out by the United Kingdom Health Agency and published on December 17 determines that the Omicron variant is detected with the same effectiveness as any of the latest variants, as is the case of the Delta. Therefore, antigen tests are just as effective in detecting the Omicron variant.
Finally, we have probably already had several tests, but do we really know what antigen tests are?
Antigen tests or tests are lateral flow diagnostic tests that detect the proteins or antigens of the virus. Generally, the test is performed by inserting a swab into both nostrils (there are also saliva detection swabs) on which antibodies have been attached that react against the protein that surrounds the virus, protein S. Through rubbing on the side wall of the nostril, the viral particles will bind to the antibody, if any. The antibody is somehow capturing the virus. Finally, by dipping the swab into the fluid containing the antigen kit, another antibody film is re-attached. A positive result indicates the presence of virus proteins.
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