How does the antigen test for COVID-19 work? How does the RT-PCR differ from a respiratory swab?

How does the antigen test for COVID-19 work? How does the RT-PCR differ from a respiratory swab?

Antigen tests are the same basis for determining coronavirus infection as RT-PCR respiratory swab, allowing faster testing of symptomatic individuals. What does such a test consist of and how does it differ from a PCR test?

What is an antigen test?

The antigen test is a rapid chromatographic immunoassay for detecting the SARS-CoV-2 antigen in the human body. It is designed for early diagnosis of infection in patients who have characteristic symptoms of coronavirus. With the ability to obtain a result in just a few minutes or so, the test is used as a rapid diagnostic tool, and its efficiency is as high as 80%.

The test has a high specificity, which indicates active infection with SARS-CoV-2 with high probability. In symptomatic individuals, a positive result can be confirmed by RT-PCR respiratory smear, but it is not necessary to refer an infected person for isolation. In patients who are asymptomatic but receive a positive antigen test, a smear is recommended. Asymptomatic individuals who receive a negative result should also complete an RT-PCR smear, as the antigen test does not provide 100% certainty that they are healthy. On the other hand, asymptomatic people with a negative result who are suspected to be in the early stages of the disease can complete a smear, as the antigen test may not yet have shown the presence of the SARS-CoV-2 virus in their body.

The antigen test visually closely resembles a pregnancy test. Its positive result is evidenced by the characteristic two lines, which, in the case of the presence of the SARS-CoV-2 virus, appear on the plate within 5 – 8 minutes after the material collected from the nasopharynx is placed on it.

Antigen test vs. PCR smear

Both the antigen test and the RT-PCR respiratory swab can be performed in patients with clinical signs of coronavirus and in those who have had contact with an infected person or have been in areas at high risk of infection. Materials for both tests are collected from the nasopharynx and, in the case of the RT-PCR swab, also from the throat.

The result of the antigen test appears on a special plate in up to a few tens of minutes, making it a very fast and helpful diagnostic tool especially in health care centers. You have to wait up to several days for the result of the genetic test, which is an RT-PCR smear, but it confirms unequivocally the infection with SARS-CoV-2. The test is recommended by the World Health Organization.

Testing for coronavirus at home

BIOCREDIT COVID-19 Ag antigen test has joined uPatient’s offer and can currently be ordered in the same way as other blood tests. During a home visit, our specialist will take a nasopharyngeal swab from the patients enrolled for the test, and then place it in the appropriate spot on the test plate. After a few minutes, a result will appear, indicating whether the patient is currently infected with the SARS-CoV-2 virus.

Read: Antigen tests for companies a chance to quickly verify the health of employees

Interpretation of the results of the antigen test

  • Negative result: only one red control line (C) appeared on the test.
  • Positive result: two lines appeared in the result window – a red control line (C) and a black test line (T).
  • Invalid result: when the red control line did not appear on the test, the test is considered invalid. This may be due to an incorrect collection procedure or mean that the test is damaged. In such a situation, it is recommended to retest the sample.

Remember that the intensity of the color and width of the line does not matter!


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