Pharmacy tests fail one in four positives due to Covid: what are the most reliable tests?

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Family parties have triggered the sale of

self-diagnosis kits

.

However, experts warn of the false sense of security that a negative in this test can provide, which misses one in four positives.

What type of

is best in each situation?

What

Are The Most Reliable?

In which cases should we perform a Covid test?

There are three situations in which it

should become a

of

: if you have had contact with an infected person, if we

detect the onset of symptoms that suggest we could have

and when we want to

prevent a possible infection before a meeting with vulnerable people.

Those vaccinated with two or three doses can also become infected, although with much less probability than those not vaccinated, and they can also infect, albeit to a lesser extent.

Of course, they are 95% protected from developing a serious disease.

In this way, vaccinated people can do without taking a

if they do not have symptoms or have had close contact.

What type of test is best for each situation?

The

is the type of

most reliable way

to diagnose an infection by

.

It is performed on a sample taken at the oropharyngeal level and the margin of error is practically nil, since the presence of the viral genome is detected even in subjects with a low load, presymptomatic or asymptomatic.

The

are sensitive to viral proteins.

There are different types, from lateral flow immunochromatographs to immunofluorescent reading tests, that offer better performance.

State-of-the-art microfluidic reading immunofluorescence tests appear to show results comparable to PCR if performed correctly.

"The

has a false negative range between 10 and 25%, depending on whether it is carried out by an expert or not," explains

, president of the

and the

.

"This means that with a

is a risk of having inaccurate results in one out of four cases, since positivity is not detected. It happens because it is not easy to correctly perform the nasal oropharyngeal sampling by oneself because, as we already know , causes some discomfort.

And the saliva ones?

are

not recommended, as they do not meet the minimum acceptable levels of sensitivity (the ability to detect a positive) and specificity (the ability to detect a negative).

Therefore, they are excluded from the European list of valid tests to obtain the Covid passport.

"The quality of the saliva sample is subject to many variables, for example the time elapsed since the food or drink and the way in which the sample was taken", Clerici emphasizes, "in general, tests of this type offer less guarantees than those that analyze an oropharyngeal nose sample. "

What is a serological test?

It is a test that measures the presence or absence of antibodies in the blood, but without measuring the amount.

If antibodies are present, it does not indicate whether the infection is ongoing or has occurred in the past.

When is it necessary to undergo a serological test?

At this time it is not useful to perform this test, unless requested by a doctor, not even with an eye to

the

.

In fact, there is no standard method and therefore it is possible to obtain different results by repeating the test in several laboratories.

Furthermore, we do not know the "correlated protection" of

, which is the level of antibodies required to defend against infection.

According to the criteria of The Trust Project

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