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Antigen Testing for SARS-CoV-2: Interim Recommendation

General Recommendations

Antigen tests are immunoassays which detect the presence or absence of a specific viral antigen. This indicates that someone is infected. Testing for antigens is possible on nasal swab samples that have been directly injected in the extraction buffer or reagent. The current approval of antigen tests is for use in many tests, including laboratory-based, self-testing, and point-of-care. They can be used by anyone of any age.

When used to screen, both the antigen test results and NAATs must be correctly interpreted. This will allow for accurate treatment of patients and people suspected of having COVID-19. It also allows for diagnosis of infected persons.

The circumstances under which antigen rapid diagnostic tests are administered or performed can greatly impact their clinical performance. Both antigen tests and NAATs are most effective when the viral load of the patient is at its highest. Antigen tests work best when people are symptomatic and within a specified time period after symptoms onset. Therefore, people with symptoms are often tested for antigens. Antigen tests can also be used to diagnose cases where the patient has been exposed to COVID-19.

Data on how antigen tests are performed in different circumstances have helped to guide the use of these tests for screening in symptomatic patients to exclude or detect SARS-CoV-2.

Performance of SARS-CoV-2 antigen testing

Healthcare providers and testing personnel should be able to identify the performance characteristics of each antigen test used. This includes its specificity, sensitivity, specificity and positive predictive values. They also need to adhere to the instructions for use provided by the manufacturer.

Although they have different levels of sensitivity, antigen tests are generally less sensitive than laboratory-based NAATs. Antigen levels in specimens taken before symptoms appear or later in the course may fall below the detection limit of the tests. A negative result may be the result of an antigen test. However, a more sensitive test such as most NAATs may give a positive result. Studies external icon show that antigen tests are similar to laboratory-based NAATs when there is a high viral load. This means that the person who is most infectious is likely to have the highest sensitivity.

Antigen tests for SARS-CoV-2 are being processed.

CLIA-certified laboratories and testing sites must comply with the manufacturer's instructions while performing the test and interpret the results. Access to the FDA's In Vitro diagnostics EUAsexternal icon gives access to both the instructions for each test and other information.

Evaluation of the Antigen Testing for SARS CoV-2 Results

When evaluating an antigen testing result, it is important to determine if the patient has ever had symptoms and for how long. Healthcare professionals can trust a positive antigen result for symptomatic patients; today, the accuracy of FDA-authorized antigen tests is high.

The FDA-approved antigen tests currently in use have different degrees of sensitivity. Therefore, it is important to treat negative results differently depending on the circumstance.

Read More : Tests For Covid-19 & PCR

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