Antigen Test – What is the Covid-19 antigen test?
The rapid antigenic test (RAT) or antigen test looks for the presence of Sars-Cov-2 virus proteins in the sample and requires the same nasopharyngeal swab as the PCR test but involves a simplified analysis technique.
The test consists of a manual test, read directly on a small plastic box, like pregnancy tests sold in pharmacies. The result is displayed in a maximum of 30 minutes in the form of bars which appear on the box.
In summary :
A positive antigen test = a Covid-19 infection
A negative antigen test = undetermined result
A negative antigen test only gives false certainty.
What is the Covid-19 antigen test used for?
This test can confirm the presence of the virus when the test is positive. Its advantage lies in the speed of rendering of the result, however it has a lower sensitivity than the PCR test, which is why it is recommended only for symptomatic cases with a high viral load.
When to perform a Covid-19 antigen test?
The Rapid Antigenic Test is useful when dealing with a person who has symptoms related to COVID (cough, fever), as it can quickly make the diagnosis of SARS-CoV-2 infection. It can be performed in a doctor’s office, in a pharmacy, at a nurse’s or in an emergency department.
It is unnecessary in people without symptoms as an individual screening.
What is the significance of a positive test?
Positivity affirms infection, with a significant viral presence. The person is therefore infected and infectious vis-à-vis the virus. RAT has very good specificity, which means there is no false positive. It is not necessary to test a positive TRA by a PCR test.
What is the significance of a negative test?
Individually, a negative TRA does not rule out the fact that the person is a carrier of Sars-Cov-2, due to the low sensitivity of these tests. Collectively, it is absolutely essential to continue to protect oneself and to protect others by respecting barrier gestures.
In the event of symptoms suggestive of Covid-19, it is necessary to perform a PCR test which is more sensitive.
“It is very important to understand that a negative test does not mean that there is no virus. There is no assurance if the Test is negative.”
What to do after this test?
If the antigen test is positive, you are sick, isolate yourself as soon as possible. Contact your doctor, identify and warn people with whom you have recently been in contact to prevent the spread of the virus. If your test is negative, congratulations! you should stay this way. For patients at risk (patients over 65 years of age or over, or presenting at least one risk factor): it is recommended to consult a doctor and confirm this result by an examination for the detection of the SARS-CoV-2 genome by PCR.
How is the Antigen Rapid Test Procedure carried out?
Tutorial or sampling procedure:
A) Sample collection: insert sterile swab through the nostril parallel to the palate, until it is in contact with the nasopharynx. Gently rub the cotton roll and remove it from the nasal cavity.
B) Insert the cotton swab into the extraction buffer and rotate it for about 10 seconds. Remove the cotton swab while squeezing the sides of the tube to extract as much liquid as possible.
C) Add 3 drops of the extracted specimen to the sample well. Wait 15 minutes and read the result. After 20 minutes have elapsed, the result should no longer be legible.
How does the Rapid Test Antigen (COVID-19 antigen rapid test) work?
The COVID-19 Antigen Rapid Test is a qualitative membrane-based immunoassay (a biochemical test that measures the concentration of substances in biological fluids) to detect the SARS-CoV-2 Antigen in swab specimens of the human nasopharynx.
SARS-CoV-2 antibody was coated in the test line region. When the extracted swab sample is applied, it reacts with the SARS-CoV-2 antibody-coated particles in the cassette. The mixture then migrates upward on the membrane by capillary action and reacts with the SARS-CoV-2 antibody in the test line region.
If the sample contains the SARS-CoV-2 Antigen, a colored line will appear in the test line region. If the sample does not contain the SARS-CoV-2 antigen, a colored line will not appear in the test line region, indicating a negative result.
ANTIGENIC, CLASSIC PCR: WHAT DIFFERENCE?
Like the Classic PCR tests, these antigenics tests are new, faster tests are performed by taking a swab from the nose. The difference is that they are much faster and allow you to read the results, like a pregnancy test, in 15 to 30 minutes.
While the classic tests look for the genome of the virus (RNA), the antigenic tests look for, as the name suggests, the antigen present on the surface of the virus (the Spike and N proteins are used as a marker).
The particles collected at the bottom of the nose are mixed with a reagent deposited on a strip. The color change makes it possible to quickly determine whether the person has Covid or not.
Photo credit: dronepicr / Wikimedia Commons
Photo descriptions: Antigen test device.