SARS-CoV-2 (Covid-19): Rapid Antigen Test for Diagnosis

SARS-CoV-2 (Covid-19): Rapid Antigen Test for Diagnosis

For rapid detection of the SARS-Cov-2 virus in 15 minutes during Covid-19 infection in nasopharyngeal specimens

COVID-19 (Corona Virus Disease) is an infectious disease caused by the most recently discovered coronavirus, SARS-CoV-2 (2019-nCoV).

Although the RT-qPCR technique is the official technique for the diagnosis of COVID-19, there are other methods available such as serological tests, rapid salivary tests and antigenic tests.
Antigenic tests are the most recent tests developed for the diagnosis of COVID-19. They are rapid tests designed to detect antigens of the SARS-CoV-2 virus, i.e. proteins present on the surface of the virus. The test is performed on a nasopharyngeal swab specimen as in the RT-qPCR tests. However, although the sensitivity of antigenic tests is lower than for RT-qPCR tests, they have the advantage of being faster (15-30 minutes) and less expensive. In addition, like serological tests, they do not require any special equipment.
Antigen rapid tests are based on the principle of immuno-chromatography as are serological tests. Antibodies directed against the SARS-Cov-2 virus antigens (usually the nucleocapsid protein or N protein) will detect the virus in the nasopharyngeal sample. A positive result with an antigen test will need to be confirmed by an RT-qPCR test.

What are the advantages of the Rapid tests :

  • Fast results in 15 minutes.
  • Detection without any specific equipment
  • Easy to use : 3-4-step simple protocol, no sample pre-treatment required
  • Efficient case tracking :  Immediate results allow an earlier start on contact tracing and isolation.
  • Compatible with nasopharyngeal and oropharyngeal swabs
  • Storage at room temperature.

What is the principle of rapid antigenic tests for the diagnosis of COVID-19?

The COVID-19 rapid antigen test detects viral antigens of the SARS-CoV-2 virus by visual interpretation with the appearance of colored lines. Anti-SARS-CoV-2 antibodies are immobilized on the test region of the nitrocellulose membrane. Anti-SARS-CoV-2 antibodies conjugated to the colored particles are immobilized on the conjugate buffer. A specimen is added to the extraction buffer which is optimized to release antigens from the SARS-CoV-2 virus present in the specimen.
During testing, the extracted antigens bind to the anti-SARS-CoV-2 antibodies conjugated to the stained particles. As the sample migrates along the strip by capillary action and interacts with the reagents on the membrane, the complex is captured by anti-SARS-CoV-2 antibodies in the test region. 
The presence of a colored band in the test region indicates a positive result for SARS-CoV-2 viral antigens, while its absence indicates a negative result. A colored band in the control region serves as a procedural control, indicating that the appropriate sample volume has been added and the membrane is functioning.

Interpretation of results