Viral tests that detect active COVID-19 infections are normally conducted using a sample that comes from your respiratory tract. A swab taken from your nose or throat is common, although some options exist for saliva testing.

There are two main types of these diagnostic or screening tests:

Molecular COVID-19 tests: Also known as nucleic acid amplification tests (NAATs), molecular tests look for genetic traces of SARS-CoV-2. By first making many copies of the genetic material in your test sample, these tests can find even very small amounts of the virus’s genetic material. There are many types of NAATs, but the most common and well-known uses a laboratory method called reverse transcription polymerase chain reaction (RT-PCR), which is sometimes referred to as PCR.

Antigen tests: Antigens are a type of protein that provokes an immune response, and antigen testing looks for antigens that are specific to SARS-CoV-2.

These tests can be performed in a laboratory setting and may be available for point-of-care or at-home testing as well. Some of these viral tests are designed to be rapid tests while others require more time to analyze.

Testing for past infections is also known as serologic testing or antibody testing. It analyzes a sample of your blood to see if there are antibodies to SARS-CoV-2. Antibodies are a protein that the immune system makes to help identify and defend against pathogens like viruses. It generally takes several weeks for some antibodies to develop, so these tests are usually not effective for detecting active infections.