For COVID-19, point-of-care (POC) tests are performed at or near the location where the specimen is collected and results of the testing can be obtained within minutes rather than hours or several days. These tests can be NAAT, antigen, or antibody (serology) testings. Rapid POC tests are available to generate results within minutes and can be used to diagnose current or past SARS-CoV-2 infections. Typically, rapid POC tests are performed in physician offices, urgent care facilities, pharmacies, health clinics, long-term care facilities, and nursing homes, and temporary locations such as drive-through sites.
The laboratory or testing site must use a test authorized for POC use by the FDA. (The FDA has issued EUA approval for several POC and rapid POC tests for SARS-CoV-2 authorized for use in a POC setting). All FDA authorized POC tests for current SARS-CoV-2 infection are intended for use on symptomatic people, however, CMS has recently indicated that POC and rapid POC testing will temporarily be allowed for CLIA-certified labs and other testing sites for use on asymptomatic people for the duration of the COVID-19 public health emergency.
The use of rapid POC viral antigen tests has gained widespread acceptance as an alternative method for the diagnosis of COVID-19 outside of health care settings. These tests differ from molecular testing such as RT-PCR in that they are designed to detect the presence of viral proteins using simple immunochromatography methods, commonly referred to as lateral flow immunoassay (LFIA). Rapid antigen tests typically detect the SARS-CoV-2 nucleocapsid protein, the most abundant protein expressed by the virus. They directly identify the presence of viral proteins, making them different from rapid antibody serology tests, which look for antibodies produced by the host in response to the infection. Thus, rapid antigen tests are used to identify acute infection only, not prior infection or response to vaccination.
The rapid POC antigen tests can offer several distinct advantages over molecular assays (such as RT-PCR) and include the following:
Rapid antigen testing can be performed outside of hospital laboratories, and many can be performed by members of the general public.
They are relatively inexpensive compared to RT-PCR and simple to interpret with a turnaround time as fast as 15 minutes
Typically, samples can be taken from the anterior nares rather than the nasopharynx thereby making them more comfortable for serial testing.
One of the disadvantages of the rapid antigen tests is the analytical sensitivity of the assay. Typically, the sensitivity of rapid antigen tests is 30-40% lower than for RT-PCR tests, depending on whether subjects were symptomatic or asymptomatic. The lower sensitivity for the test could produce an increase in the risk of false-negative results especially in people with low viral loads who may be in an early stage of their infection. Studies have shown that a majority of false-negative results usually occur in people with low amounts of the virus. It should be noted that serial testing using rapid POC viral antigen tests can help to improve the sensitivity and identify infection during the critical early transmission period.
