Early in the COVID-19 pandemic, finding a clinical laboratory to perform testing for SARS-CoV-2 seemed like a herculean challenge. There were no commercially available tests for COVID-19, and the Centers for Disease Control and Prevention (CDC) had just circulated tests that turned out to be flawed. Eventually, the CDC corrected the problems. But, there was such a concern that there were not enough diagnostic tools available that the American Society for Clinical Pathology (ASCP) wrote the FDA, urging them to allow clinical laboratories to develop (and perform) their own tests. The FDA said yes.
Out of a desire to expand test capacity and access to testing for COVID-19, the Food and Drug Administration granted emergency use authorization (EUA) of several at-home tests. This allowed individuals to walk into pharmacies or retail stories to purchase the test, go home and take a nasal swab specimen, follow the manufacturer’s instructions, and then wait for the test kit to provide the results.
These tests provided fast results. But did they provide sufficient guidance to the user?
According to Gary W. Procop, MD, MS, MASCP, Chair of ASCP’s Commission on Science, Technology and Policy, these at-home COVID-19 tests provide highly accurate positive results in individuals who are symptomatic, based on a limited amount of data submitted to the FDA. If a person who is symptomatic tests positive, they can isolate themselves from others and, thereby, prevent the spread of the virus.
However, if a symptomatic individual tests negative, how would they know to question the test results? In this instance, the results of the at-home tests should be questioned because these tests are usually less accurate than the advanced molecular tests performed in the laboratory, Dr. Procop said.
Conversely, asymptomatic individuals who receive a positive test result from a test approved for at-home use should confirm that result with an alternative assay, like a laboratory-based test. Asymptomatic individuals who are awaiting the results of a confirmatory test should maintain isolation precautions until the test results are known, in the event their test result is not a false positive.
The home test kits primarily use either isothermal amplification of nucleic acids in a process that accumulates nucleic acid sequences at constant temperature or the detection of viral proteins (ie, an antigen detection test). In contrast, reverse transcription polymerase chain reaction (RT-PCR) tests, which represents most laboratory-based tests, use sophisticated nucleic acid extraction to enhance the sensitivity of the assay, in conjunction with thermal cycling equipment for nucleic acid amplification.
The positive aspects of at-home tests include ease of use and fast results. It is also a public health advantage to keep potentially infected individuals at home for testing, rather than traveling into the community for testing. Manufacturers have provided video or online guidance to help individuals both obtain a quality specimen, appropriately perform the test, and understand the results. Some home COVID-19 tests have smartphone apps that record the results, two of which even have a mechanism for reporting results to public health departments.
There are three potential disadvantages to home COVID-19 testing. These involve specimen quality, test sensitivity, and test result interpretation. Regardless of whether a test is performed in the home or the laboratory, the first step to assure a reliable result is a high-quality specimen. It is therefore imperative the individuals carefully follow the manufacturer’s instructions. Although these tests are very good, they are not quite as sensitive as tests used in the laboratory. These at-home tests perform best on symptomatic individuals. If a person has the symptoms of COVID-19, but tests negative, then they should talk to their provider regarding a laboratory-based follow-up test. Finally, the interpretation of a negative test in an asymptomatic individual is challenging. If the asymptomatic individual does not have an exposure history and tests negative, they are likely negative, but if they have had a recent exposure history they could be early in the course of disease with a viral load below the detectable limit of the assay. If questions arise from at-home COVID-19 testing, the users should reach out to their healthcare providers with questions.