Covid: The reason an antigen test comes back positive with orange juice

Some WhatsApp users have notified on social networks that they have received some videos that in theory, They show how vulnerable and unreliable antigen tests can be to detect Covid.

This is not something new because other videos have been circulating for months now that also questioned the reliability of these tests.

In case you haven’t seen it, the clip making the rounds on the internet shows a person squeezing an orange directly onto the antigen test; in some others you can see the same action only using apple juice, tap water, beer and even urine.

The result shown in these tests is positive, so they send a message to people about this type of test that seems to be a complete hoax, thus sowing doubts among the population.

Misinterpretation of Covid antigen test videos

Although in the video you can see 2 marked lines and we can think that the result is positive, in reality the result what you are throwing is an «invalid» result, since the test application instructions were not followed. The reagent liquid inside the box, the buffer, is not used, nor is a nasal sample collected with the swab.

The 2 lines are marked by a pH issue. These tests are very sensitive since the proteins it contains need very specific conditions to function properly. The buffer, the reagent, is responsible for maintaining the sample that we deposit on the test within these optimal conditions, which will correct the pH of the sample so that it is in the appropriate range.

If we use anything as a sample, and above we do not use the reagent, the result will be totally unexpected; being able to mark one line, two or none.

These tests also include a liquid that is a necessary reagent for proper function. It is the one in charge of giving it a liquid form so that the strip of paper that comes in the kit can absorb it.

The strip is made of nitrocellulose and is impregnated with modified antibodies labeled with a colored substance. The drops of the reagent mixed with the nasal sample are deposited in the lower part of the strip, and the liquid rises by capillarity along the strip.

But the reagent has a range of efficacy, if we use it with another very acidic or very basic liquid it will exceed the effect of the buffer and will not be able to correct the pH of the sample.

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