When antigenes administered to the  organizm, they cause the immune systems reactions against them and this reaksiyon is the reason why moleculess that form a complex with antibodies.

Antigens can be microorganisms, as well as fats, carbohydrates, chemicals, enzymes, mostly proteins which are foreign to the organism.

Antigen tests are also the tests that check whether there are proteins of the virus that make up the Covid-19 disease in the patients body.

Althoug antigen test gives faster results and is more economical than pcr test it is not preferred. Because the result of a negative antigen test is not reliable and if the physician has Covid-19, he or she recommends a repeat test or a PCR test.