The Centers for Disease Control and Prevention (“CDC”) defines three different types of testing for SARS-CoV-2: Diagnostic, Screening, and Surveillance testing.  

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Diagnostic testing is intended to identify the current infection in individuals.  It should be performed when a person has signs or symptoms of COVID-19 or when an individual is asymptomatic but has had recent known or suspected exposure to SARS-CoV-2.  Some examples of diagnostic testing include testing someone who is symptomatic, testing a person identified through contact tracing, and testing someone who has indicated that they were exposed to a person with a confirmed or suspected case of COVID-19. 

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Screening testing is used to identify infected people who are asymptomatic and without known or suspected exposure to SARS-CoV-2.  Screening testing is intended to identify individuals who may be contagious so that measures can be taken to prevent further transmission.  Examples of where screening testing would be performed include congregate settings such as a long-term care facility or correctional facility, a workplace testing its employees, or a school testing students, faculty, and staff. 

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Surveillance testing for SAS-CoV-2 is meant to monitor for a community or population-level infection and disease or characterize the disease’s incidence and prevalence.  Its intended use is to gain information at a population level, rather than an individual level.  Results of surveillance testing are only returned in total to the requesting institution.  Surveillance testing differs from screening and diagnostic testing because it is performed on de-identified specimens, so results are not linked to individuals.  Surveillance testing does not entail returning a diagnostic test result to an individual or for individual decision-making. One example of surveillance testing is a state public health department’s plan to randomly select a sample a percentage of all people in a city on a rolling basis to assess local infection rates and trends.

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RT-PCR and Rapid Antigen tests are the two available tests for SARS-CoV-2.   RT-PCR tests detect current infection in an individual by detecting viral RNA in the collected specimen.  Specimens can be acquired through nasopharyngeal swabs, nasal swabs, sputum, or saliva. RT-PCR tests have high sensitivity and specificity, but often tests must be sent to a lab for analysis.  Turnaround time for RT-PCR test results ranges from 15 minutes to 2 days.  

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Similar to RT-PCR tests, rapid antigen tests detect current infection in an individual.  Rapid antigen tests differ because they are immunoassays that detect the presence of specific viral antigens.  Specimens are collected through nasopharyngeal or nasal swabs.  Rapid antigen tests are generally less sensitive than RT-PCR tests but still have high specificity.  Rapid antigen tests are relatively easy to use and can be performed at the point-of-care with results in about 15 minutes.  It is important to note that proper interpretation of rapid antigen tests is critical for accurate clinical management of patients with suspected COVID-19 or identifying potentially infected persons when used for screening. 

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Both RT-PCR and rapid antigen tests can be used in diagnostic, screening, and surveillance testing.  Any COVID-19 assays and test systems used for diagnostic or screening testing, including antigen tests, must have received a EUA from the FDA or be offered under the policies in the FDA’s Policy for COVID-19 Tests.  All rapid antigen tests for SARS-CoV-2 authorized for use by the FDA will be included on the FDA’s list of In Vitro Diagnostic EUAs.  If rapid antigen tests are being used for diagnostic or screening testing, the laboratory and testing professionals must comply with Clinical Laboratory Improvement Amendments (CLIA) regulations.  Any laboratory or testing site that reports patient-specific test results must first obtain a CLIA certificate and meet all requirements to perform that testing. Laboratories and testing professionals conducting surveillance testing for SARS-CoV-2 with rapid antigen tests are not required to comply with the FDA and CLIA requirements.  The CDC recommends that facilities conducting surveillance testing with rapid antigen tests should choose rapid antigen tests that have been authorized for use.  All approved rapid antigen tests are listed on the FDA’s In Vitro Diagnostics EUA.  

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FDA-authorized rapid antigen tests have varying sensitivities, so negative diagnostic testing results should be addressed differently depending on the testing device’s performance characteristics.  In most cases, negative rapid antigen diagnostic test results are considered presumptive, and the CDC recommends that negative results are confirmed with an RT-PCR test if the patent is symptomatic or has had known exposure to someone with a confirmed case of COVID-19.  If negative results are being confirmed with RT-PCR testing, it should be completed within two days of the initial antigen test. Rapid antigen tests can be used in diagnostic testing on symptomatic people within the first five to seven days of symptom onset.  As previously stated, rapid antigen tests being used in diagnostic testing require a EUAs from the FDA.  If rapid antigen tests are used for screening testing, test results should be considered presumptive.  Positive rapid antigen results may not need RT-PCR confirmation, especially if they are symptomatic or have had known exposure.  When confirming positive rapid antigen test results with an RT-PCR test, the patient should isolate until confirmation.  Negative rapid antigen test results used in screening testing may not need RT-PR confirmation if the patient is asymptomatic or has no known exposures, or is part of a cohort that will receive rapid antigen tests on a recurring basis.  Rapid antigen tests used in screening testing must have a EUA from the FDA. 

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In surveillance testing, rapid antigen test results do not need confirmation because test results should not be reported back to the patients tested or to their healthcare provider, employer, etc.  Surveillance testing is performed on de-identified specimens, so results are not linked to individuals.  If at any point, the laboratory conducting surveillance testing wishes to report patient-specific test results,  they must first obtain a CLIA certificate and meet all requirements to perform testing. Rapid antigen test results from surveillance testing can be returned to the requesting institution in aggregate.  Negative test results should be reported as presumptive negative.  Rapid antigen surveillance test results should not officially be reported to health departments unless requested by the local, state, tribal, or territory health department.  If rapid antigen surveillance test results are requested, it should be reported that results are from rapid antigen surveillance testing and do not represent COVID-19 diagnostic or screening test results.  Rapid antigen test results from diagnostic and screening testing must be reported to the local, state, tribal, or territory health department.  Rapid antigen test results must be clearly distinguished from other COVID-19 tests such as RT-PCR and antibody tests when reporting to public health departments.  Complete patient demographic information should be collected and reported along with diagnostic and screening test results.  The proper LOINC code for the FDA-authorized assay must be reported as well.  The table below summarizes the key components and differences of diagnostic, screening, and surveillance testing.  

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Learn more about what the CDC has to say about COVID-19 testing.

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