Are antigen tests reliable for detecting omicron? Guide to avoid false negatives

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• Guide How to do the pharmacy antigen test

After a Christmas marked by the omnipresence in the families of

, one of the main doubts that arise, given the increasing number of false negatives by

, is: are rapid tests to detect the omicron variant reliable?

The debate is growing and experts have not yet reached a definitive and safe conclusion. It seems that, in general,

are capable of detecting

with the same margin of error as any other variant, always bearing in mind that they have a slightly lower sensitivity than PCR. In practice, however, this margin of error implies a greater number of false negatives, with the danger of spread that this entails.

There is a characteristic of

that could indeed affect these results: growing evidence indicates that

accumulates mainly in the throat and not in the nose, and this could be the reason why tests based on samples taken in the nose sometimes does not detect the variant at first. However, at the moment it is only a hypothesis.

A recent empirical study followed 30 people likely to be exposed to

in the

, and found that

could detect

cases three days earlier than

, which use nasal swabs. These results are derived from a small study and have not been peer-reviewed, but confirm the suspicions of the

, the drug regulatory agency in the US, which at the end of December warned that, although they do detect

,

can have a "reduced sensitivity".

Another study conducted in

(not yet reviewed) also shows that

infections

when saliva samples were used instead of nasal samples.

Beware of false negatives

What does this imply?

Antigen tests, which look for a specific

protein , are very effective in confirming positive cases, but when the result is negative in some cases it could be incorrect.

Be aware of symptoms and risky contacts and, if in doubt, use

or repeat the test.

That said, rapid tests can deliver results in minutes and are still an important public health tool.

There are two other practical factors that could affect

results : when the test is performed and how the sample is collected.

The

(like

) should be carried out from 48 hours after a contact considered risky up to five days later, the ideal would be to do it after 48 hours and then repeat it after 5 days.

If the test is done too soon there is a risk of having a "false negative", because in the first two days the virus is not detectable by the tests, from 48 to 72 hours it is only detectable by PCR and after 72 hours it is also detectable by antigen test.

The second problem is who collects the samples: going to a laboratory minimizes the margins of false negatives.

Covid

are quite risky because you can fail to collect samples yourself.

To minimize false negatives, research shows that antigen tests are highly accurate when performed sequentially: since the incubation period with

appears to be shorter, the faster the tests are performed the more the chances of a false negative.

The advice is to do a first quick test and then wait 24 to 36 hours for a second test.

However, in case of symptoms, the test can be done immediately.

According to the criteria of The Trust Project

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