Which is the best day to do each test and avoid false negatives

With the rise of Covid-19 cases, doubts also arose as to how to test for the virus. To avoid mistakes and to bet on a false negative chip, look in the exam window to see if you have any symptoms.

Remember that there are two conditions that require a test to diagnose or rule out Covid-19.

The first is when you have two or more typical symptoms of the disease, as shown in the list below:

  • Sukar
  • Cough
  • Fatigue
  • Loss of taste or smell
  • Torn throat
  • Headache
  • Body aches
  • Diarrhea
  • Skin or eye irritation

In this case, it is best to be isolated, even before the test or if you are unable to perform the test due to lack of availability.

Second, when you have a close relationship with someone you suspect or have already been diagnosed with covid-19.

If you do not show symptoms, use a quality mask and avoid contact with members of risk groups for 10 days, led by Moacyr Silva Junior, an infectious disease specialist from the Israelite Albert Einstein Hospital Infection Control Service, São Paulo.

When each type of test should be performed

PCR: This test is the most effective in diagnosing covid-19 because it detects the genetic material of the virus in the sample in real time. Therefore, it is indicated for those who are not infected and have not yet shown any symptoms. However, the test is more expensive, and the result is sent to you by a specialized laboratory, which can take up to 72 hours.

Collection, by nasal congestion, should be performed within eight days of the onset of the first symptom. In this case, the accuracy is more than 90% accurate, with very few false positives.

When there were no symptoms, it was perfect to have the last contact with the person who was found to be infected and to count exactly five days, says Alberto Chebabo, director of Clementino Fraga Filho Hospital, UFRJ (Federal University of Rio de Janeiro) and manager. Dasa’s medical relationship. “Consider this meeting as zero days.”

If you do not respect this window, the risk of a false negative is higher.

In cases of Influenza Syndrome (GS) or Severe Acute Respiratory Syndrome (SARS) in the acute phase of the infection, collection should be performed as early as possible. In the case of critically ill hospitalized patients, collection can be performed from the onset of symptoms until the 14th day.

Antigen: It is also called a “quick test”, which can be done directly in health facilities or pharmacies, using a nasal chip. It is indicated for those who have symptoms because it detects the virus when it is being transmitted.

To avoid a false negative, perform a test in the acute phase of the disease, that is, for people with symptoms from day 1 to day 7.

Those who had no symptoms but were in contact with infected people can take the test from the 5th day of the meeting. Since the test does not give a false positive, it serves to confirm the infection, but not to rule it out.

The advantage of this is that the antigen test is ready in 30 minutes. The downside is that if the viral load is low, there is a high risk of a false negative.

self test: It works like an antigen test, the difference is that you buy it at the pharmacy and make it at home, on your own. The so-called immunochromatographic method, which indicates the presence or absence of an antigen by color, comes in a format resembling a pregnancy test.

This is the cheapest test available. As a layman does, it is essential to follow all the instructions. The result appears in a few minutes.

It was negative, what to do?

Moacyr Silva emphasized that a false positive in tests is very rare. Therefore, if the antigen test is positive, you do not need to have a PCR to confirm the diagnosis.

When the self-test or antigen test is negative and there are symptoms, it is advisable to supplement with PCR or maintain isolation anyway.

If the PCR was negative, it could be the flu, as we are suffering from an epidemic of the flu, sinusitis, or other respiratory illnesses.

With information on texts published on 08/13/22.

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