Whenever a foreign protein from a pathogen enters your system, your antibodies are designed to protect you. Suppose it’s a new protein that your already established antibodies aren’t familiar with. In that case, your white blood cells (namely the b-cells) will continue producing antibodies until they can fight the foreign protein properly. Since this is an automatic process within our bodies, these foreign proteins are considered antigens because they are antibody generators.
Antigen tests are then used to look for these antigens and quickly detect the active infection. They usually take anywhere from 15-30 minutes to get a result.
Antigen tests can be used to test for:
Another type of antigen found is human chorionic gonadotropin in urine which is produced by cells surrounding a fetus when a person becomes pregnant. Pregnancy tests are designed to look for this particular antigen.