With SMH Laboratory Services Director Harold Vore
Since late 2020, the Food and Drug Administration has authorized a handful of COVID-19 self-test kits that consumers can use at home. Demand for these at-home tests soared when the 2021-2022 school year kicked off amid a massive surge in COVID-19 cases, fueled by the Delta variant.
The self-testing kits — including Abbott Diagnostics’ BinaxNOW, Ellume Limited’s Home Test and OraSure IntelliSwab — detect COVID-19 antigens in samples that users self-collect from the nose or mouth. They are undoubtedly convenient and easy-to-use, but can you trust the results? When should you use them? Which brand is the most reliable?
Here, SMH Laboratory Services Director Harold Vore offers insights on COVID-19 home tests and discusses the pros/cons of both antigen tests and molecular tests (PCR / NAAT).
Vore, who has 35 years’ experience in hospital-based clinical labs, is a Florida Department of Health-licensed laboratory supervisor and holds national accreditation with the American Society of Clinical Pathologists.
How do the at-home COVID-19 antigen tests differ from PCR/NAAT molecular tests?
Molecular tests, or nucleic acid amplification tests (NAAT), detect COVID-19 by hunting multiple, specific genetic targets of the SARS-CoV-2 virus that causes COVID-19. These tests are very sensitive (they can detect even very low levels of the virus) and very specific (they only detect SARS-CoV-2). But, for the most part, only federally licensed clinical laboratories can process these molecular tests.
COVID-19 antigen tests, however, use a fairly common process to detect a single SARS-CoV-2 antigen target and are more readily available. (An "antigen" is a toxin or other foreign substance that sparks an immune response in the body, usually causing the body to create antibodies.) Antigen tests are generally less sensitive and less specific than molecular methods, but they are more accessible for community members because they don’t require specialized equipment or training to use.
What You Need to Know
- At-home COVID-19 antigen tests are most reliable when symptoms are present.
- Only use DIY test kits that have FDA emergency use authorization.
- The most common reason for error is failure to follow manufacturer directions. For accurate results, read and follow product instructions carefully for sample collection, test procedure and test result interpretation.
- The accuracy of home tests is on par with that of rapid antigen tests performed at state test sites, when samples are collected properly.
- PCR / NAAT (molecular) tests are more sensitive than DIY at-home tests, so they are more likely to detect low levels of viral infection.
Can we trust results from COVID-19 self-test kits?
Yes. When performed correctly, self-testing with antigen tests can provide valuable information, particularly when testing someone who’s symptomatic. Essentially, over-the-counter test kits are as reliable as the rapid antigen tests performed at state testing sites, and during the symptomatic phase of infection, their accuracy is comparable to that of PCR/NAAT tests.
Do I need a follow-up PCR/NAAT test to confirm the results of an at-home COVID-19 antigen test?
If you have symptoms and get a positive antigen test result, you are considered positive for COVID-19 and do not need further confirmation testing, according to Centers for Disease Prevention and Control guidelines. But, if you have symptoms and get a negative antigen test result, CDC guidelines recommend confirming the result with a followup PCR/NAAT test.
When should COVID-19 self-tests be used?
At-home antigen tests can be a good choice when:
- Testing someone with symptoms.
- Monitoring groups, such as a school or workplace, for outbreaks.
- Required for travel. (Always review the test method requirements of your destination; some may require a PCR/ NAAT test and will not accept an antigen test result.)
What is the best at-home COVID-19 test kit?
While the Biofire Diagnostics molecular COVID-19 test system has earned full approval from the Food and Drug Administration (FDA), all other COVID-19 test systems (both antigen and other molecular methods) are available under FDA Emergency Use Authorization (EUA).
When buying a home test kit, choose one that has the EUA labeling. Pay attention to the stated sensitivity of the test, and be aware that the stated sensitivity is based upon less data than normally required for full FDA approval.
Click here for the FDA’s list of authorized test kits, most of which are readily available from local pharmacies in our area and from online retailers. Note that Sarasota County schools are accepting results from Ellume home test kits.
Are there any drawbacks to relying on at-home antigen test results?
Because antigen tests are less sensitive than molecular tests, they may not be able to detect COVID-19 early in the virus’ infection progression. The difference in detection capability of these different test types can range from 24 hours to 5 days, if a person is asymptomatic.
For example, if you take an antigen test because you were exposed to someone with COVID-19 a few days ago but you don’t have any symptoms, you’re more likely to get a false negative result than if you take a PCR/NAAT test.
PCR/NAAT tests have the opposite issue: Because the tests are so sensitive, they can detect virus particles up to 3 months after infection, long after the virus’ infectious stage. There have even been cases where PCR/NAAT tests detected viral particles up to 6 months after infection, but such cases are not the norm.
This means that with a PCR/NAAT test, you could test positive for COVID-19 long after recovery and even though you are no longer at risk of spreading COVID-19.
Harold Vore, MS, MT(ASCP), has served as the director of SMH Laboratory Services for the last 6 years. With 35 years’ experience, Vore is a Florida Department of Health-licensed laboratory supervisor and holds national accreditation with the American Society of Clinical Pathologists. A graduate of Indiana University, he has a BS in Medical Laboratory Science and a master’s degree in Health Care Management.