The methods of collecting the biological sample are completely similar to those of molecular tests (nasopharyngeal swab), so this type of test is also performed on the patient's respiratory secretions.
Unlike the molecular swab ("gold standard" test for the diagnosis of COVID-19), however, the antigen test does not identify specific traces of the RNA genome of the SARS-CoV-2 virus, but detects some components of the virus (Spike proteins and Nucleocapsid) indicative of the occurred exposure to the viral agent.
COVID-19 antigenic tests are cheaper and require short times to provide a response (30-60 minutes, instead of hours or days); this makes them a strategic tool that can be applied to some particular situations (for example, in the screening of passengers at airports), as an alternative to molecular swabs. The sensitivity and specificity of the COVID-19 antigen test are, however, lower than those of the molecular test, so the positivity diagnoses obtained must be confirmed by a second molecular swab.
specific able to bind to the viral antigens of the coronavirus responsible for the infection.
In practice, during the COVID-19 antigen test, specific peptides (protein portions) of the S (Spike) or N (nucleocapsid) protein present on the surface of SARS-CoV-2 are intercepted by polyclonal or monoclonal antibodies.
The result of the antigen-antibody reaction can be directly visible to the naked eye or read by means of a simple apparatus at the "point of care"(POCT), without the need to be performed in a laboratory.
