SARS-CoV-2 Antigen Test

General guidance

Antigen testing is commonly used to diagnose other respiratory pathogens, including influenza virus and respiratory syncytial virus (RSV).The U.S.Food and Drug Administration (FDA) has granted Emergency Use Authorization (EUA) for an antigen test that recognizes SARS-CoV-2,for in vitro diagnostics.Antigen tests are immunoassays that detect the presence of specific viral antigens, which indicate a current viral infection. Antigen tests are currently authorized to be performed on nasopharyngeal, nasal swab, or saliva specimens placed directly into assay extraction buffers or reagents.Currently authorized antigen tests include point-of-care, laboratory-based and self-testing.Some tests have age restrictions;Antigen tests provide rapid results (within approximately 15-30 minutes), and most are available at the point of care.Antigen detection of SARS-CoV-2 is generally less sensitive than real-time reverse transcription polymerase chain reaction (RT-PCR) and other nucleic acid amplification tests (NAAT), which detect and amplify the presence of viral nucleic acid.However, NAATs may remain positive for weeks to months after initial infection and detect levels of viral nucleic acid even when the virus cannot be cultured, suggesting that the presence of viral nucleic acid does not always indicate infectivity.

Antigen testing and NAAT (if indicated) need to be interpreted correctly for accurate clinical management of patients with suspected COVID-19 and to identify infected individuals when used for screening.The clinical performance of diagnostic tests depends largely on the environment in which they are used.Antigen testing and NAAT work best if the patient is tested at the onset of symptoms.Although antigen tests are generally less sensitive than NAATs, they can also be used to detect infection, with specific attention to the context.

Antigen test performance data can help guide the use of these tests as screening tests in asymptomatic populations to detect SARS-CoV-2 infection.Antigen tests have been used to conduct COVID-19 screening tests in congregate settings such as nursing homes, dormitories, homeless shelters, and correctional facilities.Screening tests have rapidly identified COVID-19 patients, informing infection prevention and control measures to prevent transmission.In such cases, providing immediate results through antigen testing is valuable if fast test turnaround time is critical. 

Healthcare providers and public health practitioners should be aware of test performance characteristics to interpret results, identify potential false-negative or false-positive test results, and direct additional confirmatory testing and management of subjects. Laboratories and testing professionals performing antigen testing should be aware of factors that affect the accuracy of antigen testing, as described in this guidance.Healthcare providers, laboratory and testing professionals, and public health practitioners should also understand the differences between diagnostic, screening, and surveillance tests.This guidance complements and is consistent with CDC's SARS-CoV-2 Testing Overview and SARS-CoV-2 Point-of-Care and Rapid Testing Guidance.CDC also issued guidance on SARS-CoV-2 antigen testing in long-term care facilities, interim guidance on SARS-CoV-2 testing in correctional and detention facilities, and testing in homeless shelters and encampments Interim Guidance on SARS-CoV-2 Testing, and COVID-19 Prevention Guidance for K-12 Schools.

Regulatory Requirements for Using SARS-CoV-2 Antigen Tests

FDA Regulation of In Vitro Diagnostic Devices and Coronavirus Disease 2019 Testing Policy (Revised) During the Public Health Emergency (“COVID-19 Testing Policy”) and EUA Templates Referenced in That Policy.COVID-19 tests and testing systems for diagnostic or screening testing, including systems for antigen testing,must have received an EUA from FDA or be provided in accordance with FDA's policy in COVID-19 Testing Policy.Every SARS-CoV-2 antigen test authorized for use by FDA is included in FDA's In Vitro Diagnostic EUA list.The intended use of each test, provided in the instructions for use and release letter, defines the intended population of the test,acceptable sample types, and how the results will be used.Laboratories and testing professionals using antigen tests to perform diagnostic or screening tests for SARS-CoV-2 must also comply with the Clinical Laboratory Improvement Amendments.Any laboratory or testing site that intends to report patient-specific test results to individuals or healthcare providers must first obtain certification and meet all requirements for performing the test.