involves analyzing samples to assess the current or past presence of SARS-CoV-2, the virus that cases COVID-19 and is responsible for the COVID-19 pandemic. The two main types of tests detect either the presence of the virus or antibodies produced in response to infection.^[1][2] Molecular tests for viral presence through its molecular components are used to diagnose individual cases and to allow public health authorities to trace and contain outbreaks. Antibody tests (serology immunoassays) instead show whether someone once had the disease.^[3] They are less useful for diagnosing current infections because antibodies may not develop for weeks after infection.^[4] It is used to assess disease prevalence, which aids the estimation of the infection fatality rate.^[5]

Individual jurisdictions have adopted varied testing protocols, including whom to test, how often to test, analysis protocols, sample collection and the uses of test results.^[6][7][8] This variation has likely significantly impacted reported statistics, including case and test numbers, case fatality rates and case demographics.^{[9][10][11][12]} Because SARS-CoV-2 transmission occurs days after exposure (and before onset of symptoms), there is an urgent need for frequent surveillance and rapid availability of results.^[13]

Test analysis is often performed in automated, high-throughput, medical laboratories by medical laboratory scientists. Rapid self-tests and point-of-care testing are also available and can offer a faster and less expensive method to test for the virus although with a lower accuracy.^[14][15]

Positive viral tests indicate a current infection, while positive antibody tests indicate a prior infection.^[17] Other techniques include a CT scan, checking for elevated body temperature, checking for low blood oxygen level, and detection by trained dogs.^[18][19][20]

Detection of the virus is usually done either by looking for the virus's inner RNA, or pieces of protein on the outside of the virus. Tests that look for the viral antigens (parts of the virus) are called antigen tests.

There are multiple types of tests that look for the virus by detecting the presence of the virus's RNA. These are called nucleic acid or molecular tests, after molecular biology. As of 2021, the most common form of molecular test is the reverse transcription polymerase chain reaction