Antigen and Molecular Tests for COVID-19

The diagnostic testing field for COVID-19 is rapidly evolving, with many tests focused on diagnosing patients with active viral infections. Diagnostics able to detect current, active infections are typically antigen- and molecular-based tests. These tests inform researchers and health providers of the presence of the pathogen, either by amplifying and detecting its genetic material or identifying unique markers of the pathogen itself. The viral genomic material for SARS-CoV-2 is ribonucleic acid (RNA), which remains in the body only while the virus is still replicating, even at very low levels.

Antigen tests detect specific viral proteins (antigens) present in a patient sample taken using nasal or nasopharyngeal swabs and can provide results in under a half hour. Antigens are found on the surface of the virus particle, which are also shed in patient tissues. These rapid tests detect basic levels of antigen already present in a sample, providing only a simple “yes” or “no,” similar to a pregnancy test.

Molecular tests called nucleic acid amplification tests (NAAT) rely on amplification of existing genetic material in the sample. NAATs include the polymerase chain reaction (PCR) assay in a laboratory to amplify viral genomic material for detection and can provide results in hours to days; other techniques include LAMP and next generation sequencing. These tests require samples from the patient that are likely to contain virus. Most samples are collected using nasopharyngeal swabs or a sputum cup, although the virus may also be detected in feces, urine, or blood. For diseases that are primarily respiratory in nature, like COVID-19, nasopharyngeal swabs have been the most reliable, as they sample an area of the respiratory tract where the virus appears to first infect an individual. This site is relatively easily accessed, compared to the final site of viral infection: the lower respiratory tract. The nasopharyngeal tract likely has (1) active virus replication and (2) enough virus to be detected in test kits.

Many tests now available or in development can use saliva or nasal swabs that facilitate easier sampling procedures for healthcare providers and patients.

For information on serology (antibody) tests, visit our serology tracker or visit our report outlining the needs of a national serology strategy.

Disclaimer

This page is updated twice weekly and includes only tests that have received EUA either from commercial manufacturers or laboratory-developed tests. This website is not intended to be used as a reference for funding or grant proposals. Noninclusion in this list should not be interpreted as a judgment on the validity or legitimacy of tests.

If you are a manufacturer or research institution that has an EUA-approved antigen or molecular test that is not yet listed, please submit your information here. Submission of this form does not guarantee inclusion on the website.

Note on sensitivity and specificity data

Where available, we list the manufacturer-reported sensitivity and specificity data. A highly sensitive test should capture all true positive results. A highly specific test should rule out all true negative results. These measures are not independently validated by the Johns Hopkins Center for Health Security. If sensitivity or specificity is not listed, it was not available from the manufacturer at the time of posting. When available, the number of samples used for sensitivity/specificity definitions are listed in the product description.

The terms “sensitivity” and “specificity” may not appear in the manufacturers’ information sheets, but are often reported as “positive percent agreement” and “negative percent agreement.“ Sensitivity may also be measured by calculating the limit of detection, which is the lowest detectable number of virus copies in a sample at which the test will return a positive result at least 95% of the time. Essentially, a lower limit of detection indicates a more sensitive test, with fewer viral copies per sample necessary to elicit a positive test result. The US FDA recommends that manufacturers use these terms to indicate that a nonreference standard was used when evaluating the test.

More information on molecular tests:

• How do molecular tests detect SARS-CoV-2?
• Types of molecular tests being developed for SARS-CoV-2