Healthcare Workers

Considerations When Testing

SARS-CoV-2 testing may be incorporated into a comprehensive approach to reducing transmission that also includes screening for symptoms and contact tracing. When combined, these strategies can identify people infected with SARS-CoV-2 so that actions can be taken to slow and stop the spread of the virus.

People undergoing testing should receive clear information on

• The manufacturer and name of the test, the type of test, the purpose of the test, the performance specifications of the test, any limitations associated with the test, who will pay for the test, how the test will be performed, how and when people will receive test results, and;
• How to understand what the results mean, what actions need to happen after someone has negative or positive results, the difference between testing for workplace screening versus for medical diagnosis, who will receive the results, how the results may be used, and any consequences for declining to be tested.

Individuals tested are required to receive patient fact sheets as part of the test’s Emergency Use Authorization (EUA).

Vaccination and SARS-CoV-2 Testing

If a person has received a COVID-19 vaccine, it does not affect the results of their SARS-CoV-2 viral tests (nucleic acid amplification tests [NAAT] or antigen). Because the Pfizer-BioNTech, Moderna, and Johnson & Johnson COVID-19 vaccines use the SARS-CoV-2 spike protein to generate an immune response, a positive serologic (antibody) test for spike protein IgM/IgG could indicate either previous infection or vaccination. Antibody testing is not currently recommended to assess for immunity to SARS-CoV-2 infection following COVID-19 vaccination or to assess the need for vaccination in an unvaccinated person. To evaluate for evidence of previous infection in a vaccinated individual, an antibody test specifically evaluating IgM/IgG to the nucleocapsid protein should be used (e.g., for public health surveillance or the diagnosis of Multisystem Inflammatory Syndrome in Children (MIS-C) or Multisystem Inflammatory Syndrome in Adults (MIS-A)). For guidance on quarantine and testing of people who are up to date with their vaccines, please visit COVID-19 Quarantine and Isolation | CDC.

Testing for SARS-CoV-2 Infection

Many types of tests are used to detect SARS-CoV-2,¹ and their performance characteristics vary.

• Some tests provide results rapidly (within minutes); others require time for processing.
• Some must be performed in a laboratory by trained personnel, some can be performed at the point of care, and others can be performed at home or anywhere.
• Some tests are very sensitive (i.e., few false-negative results or few missed detections of SARS-CoV-2); others are very specific (i.e., few false-positive results or few tests incorrectly identifying SARS-CoV-2 when the virus is not present); and some are both sensitive and specific.
• Some tests can be performed frequently because they are less expensive and easier to use than other tests, and supplies are readily available.

When selecting which SARS-CoV-2 test to use healthcare providers, public health professionals, and those organizing and implementing testing should consider  the context in which they are being used, including the prevalence of SARS-CoV-2 in the population being tested (See Table 1) and the status (signs, symptoms, close contacts) of the person being tested.

Test Types

Viral tests, including Nucleic Acid Amplification Tests (NAATs, such as Reverse Transcription – Polymerase Chain Reaction) and antigen tests, are used as diagnostic tests to detect current infection with SARS-CoV-2 and to inform an individual’s medical care. Viral tests can also be used as screening tests to reduce the transmission of SARS-CoV-2 by identifying infected persons who need to isolate from others. See FDA’s list of In Vitro Diagnostics Emergency Use Authorizationsexternal icon for more information about the performance of specific authorized tests.

• NAATs are high-sensitivity, high-specificity tests for diagnosing SARS-CoV-2 infection. NAATs detect one or more viral ribonucleic acid (RNA) genes and indicate a current infection, or can indicate a recent infection due to prolonged viral RNA detection. NAAT results are not always direct evidence for the presence of virus capable of replicating or being transmitted to others. Most NAATs need to be performed in a laboratory, however some are point-of-care tests, and a few are self-tests. Time to results can vary by laboratory test (~1–3 days), but point-of-care or self-tests NAATs can produce results in about 15–60 minutes. Most NAATs produce qualitative results. NAATs can be performed on upper respiratory specimens, such as nasopharyngeal, nasal mid-turbinate, anterior nasal, or saliva.
• Antigen tests are immunoassays that detect the presence of a specific viral antigen. Antigen tests generally have similar specificity, but are less sensitive than most NAATs. Most are less expensive than NAATs and can provide results in minutes, making them useful in screening programs to quickly identify persons who are likely to have COVID-19. There are antigen tests available for at-home testing (self-testing), at the point of care, or in a laboratory. Because of the performance characteristics of antigen tests, it may be necessary to confirm some antigen test results (a negative test in persons with symptoms or a positive test in persons without symptoms) with a laboratory-based NAAT. Some point-of-care NAATs that provide presumptive results cannot be used for confirmatory testing. Use of the Antigen Testing Algorithmpdf icon is recommended to determine when confirmatory testing is needed.

Correct interpretation of results from both antigen tests and confirmatory NAATs, when indicated, is important.

Positive test results allow for identification and isolation of infected persons, as well as a case interview to identify and notify the case’s close contact(s) of exposure and the need to quarantine.

Negative test results in persons with known SARS-CoV-2 exposure suggest no current evidence of infection. These results represent a snapshot of the time around specimen collection and could change if the same test was performed again in one or more days. For guidance on quarantine after a negative test, visit COVID-19 Quarantine and Isolation | CDC. In healthcare facilities with an outbreak of SARS-CoV-2, recommendations for viral testing of healthcare providers, residents, and patients (regardless of their vaccination status) remain unchanged.

Negative test results in persons who have no symptoms and no known exposure suggest no infection. All persons being tested, regardless of their results, should talk to their healthcare provider about risk reduction behaviors that help prevent the transmission of SARS-CoV-2 (e.g., wearing a well-fitting mask, physical distancing, avoiding crowds and poorly ventilated spaces).

Antibody (or serology) tests are used to detect previous infection with SARS-CoV-2 and can aid in the diagnosis of multisystem inflammatory syndrome in children (MIS-C)external icon and in adults (MIS-A)². CDC does not recommend using antibody testing to diagnose current infection. Depending on the time when someone was infected and the timing of the test, the test might not detect antibodies in someone with a current infection. In addition, it is not currently known whether a positive antibody test result indicates immunity against SARS-CoV-2; therefore, at this time, antibody tests should not be used to determine if an individual is immune against reinfection. Antibody testing is being used for public health surveillance and epidemiologic purposes. Because antibody tests can have different targets on the virus, specific tests might be needed to assess for antibodies originating from past infection versus those from vaccination. For more information about COVID-19 vaccines and antibody test results, refer to Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States.

Overview of Testing Scenarios

Diagnostic testing is intended to identify current infection in individuals and is performed when a person has signs or symptoms consistent with COVID-19, or is asymptomatic, but has recent known or suspected close contact exposure to SARS-CoV-2.

Examples of diagnostic testing include:

• Testing persons with symptoms consistent with COVID-19, whether or not they are up to date on their vaccinations.
• Testing persons as a result of contact tracing efforts.
• Testing persons who indicate that they had close contact exposure with someone suspected or confirmed as having COVID-19.

Screening tests are recommended for those who have no symptoms and no known, suspected, or reported close contact exposure to SARS-CoV-2. Screening helps to identify unknown cases so that measures can be taken to prevent further transmission.

Examples of screening include:

• Testing employees in a workplace setting
• Testing students, faculty, and staff in a school or university setting
• Testing a person before or after travel
• Testing at home for someone who does not have symptoms associated with COVID-19 and no known exposures to someone with COVID-19

Public health surveillance is intended to monitor population-level burden of disease, or to characterize the incidence and prevalence of disease. Surveillance testing is primarily used to gain information at a population level, rather than an individual level, and generally involves testing of de-identified specimens. Surveillance testing results are not reported back to the individual. As such, surveillance testing cannot be used for an individual’s healthcare decision making or individual public health actions, such as isolation or quarantine.

An example of surveillance testing is wastewater surveillance.

Choosing a Test

When choosing which test to use, it is important to understand the purpose of the testing (diagnostic or screening), performance of the test within the context of the level of community transmission, need for rapid results, and other considerations (See Table 1). For example, even a highly specific antigen test may have a poor positive predictive value (high number of false positives) when used in a community where prevalence of infection is low. As an additional example, use of a laboratory-based NAAT in a community with high transmission and increased test demand may result in diagnostic delays due to processing time and time to return results. Positive and negative predictive values of NAAT and antigen tests vary depending upon the pretest probability. Pretest probability considers both the prevalence of the level of community transmission as well as the clinical context of the individual being tested. Additional information is available on sensitivity, specificity, positive and negative predictive values for antigen tests and antibody tests, and the relationship between pretest probability and the likelihood of positive and negative predictive values[458 KB, 1 Page]. Also see FDA’s letters to clinical laboratory staff and healthcare providers on the potential for false-positive results with antigen tests and the potential for false-negative results with molecular tests if a genetic variant of SARS-CoV-2 is found in the part of the viral genome assessed by the test.

Table 1 summarizes some characteristics of NAATs and antigen tests to consider for a testing program. Given the risk of transmission of SARS-CoV-2 from asymptomatic and presymptomatic persons with SARS-CoV-2 infection, use of antigen tests in asymptomatic and presymptomatic persons can be considered. FDA has provided a list of FAQs for healthcare providers who are using diagnostic tests in screening asymptomatic individuals, and the Centers for Medicare & Medicaid Services will temporarily exercise enforcement discretionexternal icon to enable the use of antigen tests that are not currently authorized for use in asymptomatic individuals for the duration of the COVID-19 public health emergency under the Clinical Laboratory Improvement Amendments of 1988 (CLIA). Laboratories that perform screening or diagnostic testing for SARS-CoV-2 must have a CLIA certificate and meet regulatory requirements. Tests that have received an EUA from FDA for point-of-care (POC) use can be performed with a CLIA certificate of waiver.

Health Equity in SARS-CoV-2 Testing

CDC’s COVID-19 Response Health Equity Strategy outlines a plan to reduce the disproportionate burden of COVID-19 among racial and ethnic minority populations and other population groups (e.g., essential and frontline workers, people living in rural or frontier areas) who have experienced a disproportionate burden of COVID-19. One component to move towards greater health equity and to stop transmission of SARS-CoV-2 is ensuring availability of resources, including access to testing for populations who have experienced longstanding, systemic health and social inequities. All population groups, including racial and ethnic minority groups, should have equal access to affordable, quality and timely SARS-CoV-2 testing – with fast turnaround time for results — for diagnosis and screening to reduce community transmission. Efforts should be made to address barriers that might overtly or inadvertently create inequalities in testing.

In addition, completeness of race and ethnicity data is an important factor in understanding the impact the virus has on racial and ethnic minority populations. The U.S. Department of Health and Human Services has required laboratories and testing facilities to reportexternal icon race and ethnicity data to health departments, in addition to other data elements, for individuals tested for SARS-CoV-2 or diagnosed with COVID-19. Healthcare providers and public health professionals need to ask and record race and ethnicity for anyone receiving a reportable test result and ensure these data are reported with the person’s test results in order to facilitate understanding the impact of COVID-19 on racial and ethnic minority populations.

In communities with a higher proportion of racial and ethnic minority populations and other populations disproportionately affected by COVID-19, health departments should ensure there is timely and equitable access to and availability of testing with fast result return, especially when the level of community transmission is substantial or high.

Some strategies to achieve this goal include:

• Use a social vulnerability index to assist in selecting testing sites.
• Assess the capacity of these sites to expand diagnostic and screening testing to meet the demand for impacted areas. This includes assessing the availability of free testing, wait times for testing and for results, and categories of available test (NAAT vs. antigen), as well as identifying and removing barriers to testing (e.g., alternatives to drive-through testing for a community where many do not have cars; availability of testing on evenings and weekends).
• Increase the availability of free testing sites in communities. Employers, community-based, and faith-based organizations can be important partners to increase the number of free, community-based testing sites. This expansion ensures that wait times both for testing and reporting of results are decreased, helping limit the spread of SARS-CoV-2.
• Increase public messaging about the importance of testing and communicate these messages in multiple languages and venues, particularly in communities at higher risk and disproportionately impacted by the virus.