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How to do an antigen test: Guide for proper use of the antigen test: When and how should this test be done?

The rapid processing of the Ómicron variant has set off all the alarms. And more so because of the dates we are in, which has caused the tests to detect positives to reach exorbitant levels. Among these, antigen tests stand out, for sale in pharmacies. In recent weeks they have been selling out in Malaga and their price has multiplied compared to previous dates. They have become a vital tool to give some margin of peace before Christmas gatherings, but they should not be done lightly, but rather it is necessary to take into account some key points. For example, it is important to carry it out during the first seven days after infection or in the first five days after the appearance of symptoms, when the viral load is at its highest point.

They should be purchased exclusively from pharmacies, which have been officially evaluated, and to know their reliability, the levels of sensitivity and specificity should be consulted in the instructions for use. The European Union recommends using tests with a minimum specificity of 97% and sensitivity of 90%.

How do they work?

It is key to follow the instructions indicated in the leaflet. Whether it is a nasal or saliva test, to know if it has been done correctly it is important to look at the C (control) on the meter. A line should always appear. Otherwise, the test is wrong.

The test line (T) will mark whether the test is positive or negative. One line, negative. Two, positive. The result may be invalid. This will happen if no colored line appears when performing the test, or only line T is displayed, but not line C, the test is invalid and you must repeat it.

It must also be taken into account that although the test only shows the control line (C) and, therefore, is negative, infection cannot be completely ruled out, since it may happen that at that moment the viral load is too low. to be detected, since these tests have a lower sensitivity than PCR.

And the opposite case can also occur, a false positive, due to contamination of the sample or because there are some substances that interfere. To confirm whether or not it is a false positive, it is necessary to subsequently perform a PCR test. And if you have any questions, it is advisable to make an appointment to take a test at the health service.