RNA of every specie of virus is distinct. RT-PCR test determines the absence or presence of RNA genetic material of the SARS-CoV-2 virus in nasal secretion sample. It is the most accurate test to diagnose COVID-19 infection. If you require a valid report, and do not need it instantly, then getting RT-PCR test is the right option.
Rapid antigen test is a diagnostic test that checks current COVID-19 infection. This test uses sample of nasal secretions from the respiratory tract. It is most applicable for rapid testing of many individuals as its results are ready in 15 minutes. It is an over-the-counter test, so you can order it at your home too and receive results instantly. This test is less accurate than the RT-PCR test.
Both vaccinated and un-vaccinated individuals may require antibodies test for COVID-19. Antibodies form in response to a specific antigen, thereby they have distinct chemical composition. The function of the antibodies is to protect against a specific antigen, the SARS-CoV-2 virus, in case of COVID-19. Vaccine also injects antibodies. Antibodies show up in 1 to 2 weeks in COVID-19 patients and then they decrease with time. This test also helps determine the stage of infection of COVID-19 patients.