Looking For a Home COVID-19 Test? Know the Difference Between Antigen and Molecular Tests
Now that we’re well into the COVID-19 pandemic, testing is more readily available to the general public. So far, the FDA has approved over 225 diagnostic COVID-19 tests, 25 of which people can take at home – most commonly by saliva sample or nasal swab – and ship out to a lab for results, according to an agency press release. There are also currently three that the public can conduct entirely at home in as little as 15 minutes in some cases.
There’s the Ellume COVID-19 Home Test, the first COVID-19 test you complete in full in your home without a prescription, and two prescription-based tests: the BinaxNOW COVID-19 Ag Card Home Test, which requires you to download an app, and the Lucira COVID-19 All-in-One Test Kit. But just how accurate are these at-home COVID-19 tests?
What Types of FDA-Approved Home COVID-19 Tests Are There?
There are two types of COVID-19 diagnostic tests that have been approved for use by doctors and people at home: molecular tests that look for the virus’s genetic material on a sample that’s typically sent out to labs (you’ve probably heard of molecular PCR tests before) and antigen tests that detect specific proteins from the virus. Most rapid tests are antigen tests; however, it’s important to note that the FDA states some rapid tests can be molecular-based instead.
Case in point: UC Davis Health developed a point-of-care COVID-19 test that uses the PCR method. The entirely home-based tests mentioned above are antigen tests except for Lucira, which uses an alternative molecular method called “loop-mediated isothermal amplification,” or LAMP. Bottom line is that if you’re sending out a sample you’ve collected at home, as of late, you’re most likely doing a PCR test.
Are Home COVID-19 Tests Accurate?
The short answer is yes, but it also depends on if you have symptoms. Generally speaking, Amesh Adalja, MD, FIDSA, infectious-disease physician and senior scholar at the Johns Hopkins University Center for Health Security, told POPSUGAR that he thinks the home kits are designed to minimize the risk of human error if you follow the exact directions given.
PCR laboratory tests, using a method called “polymerase chain reaction,” are referred to as the “gold standard” of COVID-19 tests, and the FDA states that while antigen tests are “very specific for COVID-19,” they are not as sensitive as molecular PCR tests. “This means that there is a higher chance of false negatives than with many molecular tests,” the agency states.
Even if you’re asymptomatic, a PCR test will still detect very small amounts of the virus, but Dr. Adalja said that doesn’t necessarily mean you’re contagious. “An antigen test is much more likely to pick up, be much more accurate, when you’re talking about enough virus to infect another person,” he noted.
Though Dr. Adalja did state rapid tests are more accurate than they were in the beginning of the pandemic, they may not be as effective in detecting infection if you don’t have symptoms. “If you’re sick, you can start with an antigen test, and if it’s positive, you’ve got an answer,” he said. “But if it’s negative, you still need to do something to figure out why you’re sick.” The CDC advises people exhibiting COVID-19 symptoms who ultimately test negative with a rapid antigen test to get a molecular test to confirm those results.
Ask Yourself Which Home COVID-19 Test Is Most Effective
As Dr. Adalja explained, molecular diagnostic tests in asymptomatic individuals might not be the best home tests “because you’re going to pick up minute amounts of virus that may not reflect contagiousness.” Therefore, Dr. Adalja said you have to remember why you’re testing yourself at home: “Are you testing yourself because you have symptoms, or are you testing yourself just to know whether or not you’re contagious to somebody else?”
Michael Mina, MD, PhD, assistant professor of epidemiology at Harvard T. H. Chan School of Public Health, agreed that while PCR tests are better at detecting those small amounts of virus regardless of if you’re infectious, when it comes to effectiveness, those rapid (more likely antigen) tests are better. “I would take, for example, a rapid test that is 20 percent less sensitive but gives me an immediate result any day over a PCR test that I have to order, send back in, and get a result three days later,” he told POPSUGAR during a media call. “That PCR test is very ineffective versus a rapid test if your goal is effectiveness.”
Dr. Mina continued, “We should be exploring and asking the question ‘What’s more effective?,’ not, ‘Which is more sensitive?,’ because you can have a very sensitive test, but if it gives you a result five days later, it’s not a useful test.”
What’s the Future of At-Home COVID-19 Testing?
Limitations exist when it comes to current home novel coronavirus tests, one of them being cost and another being the fact that some call for prescriptions. “The goal needs to be over-the-counter testing, because a prescription puts a barrier,” Dr. Adalja said, adding that they need to be a lot cheaper to become more accessible as well. Ellume costs $30. Lucira, which won’t be available nationally until next spring, will cost up to $50, and BinaxNOW goes for $25. And that’s nothing compared to the home collection kits sold at major retailers – those go for $100 at minimum. (Note: depending on where you live, states in the US may be giving out home collection kits for free.)
Dr. Mina mentioned during that same media call that while the Ellume test, for instance, is a good alternative to going to the doctors if you’re symptomatic, it’s not as easily accessible as, say, low-cost paper-strip tests that he’s been pushing for as a public health tool. “We need the FDA to be recognizing that now that they have said that people don’t need to have physician involvement based on the Ellume test, I think all of the dominoes should fall, and none of these tests should be required to have physician involvement,” Dr. Mina said.
While Dr. Adalja favors saliva tests because they are less invasive and don’t require special swabs, Dr. Mina is a proponent of nasal swabs for capturing “infectious virus that’s at high viral loads.” Both said that, eventually, this concept of testing yourself every day or every few days – otherwise known as “serial testing” – is the goal.
A big gain of home tests is that you’ve “empowered people to take their health into their hands,” Dr. Adalja said, and there’s potential to get a larger amount of the public tested. Another plus? You’ll have fewer people waiting in line to get tested in doctor’s offices who might be infectious.
What Should You Do If You Test Positive For COVID-19 at Home?
No matter what, Dr. Adalja said, it’s best to speak to your doctor if you test positive and also if you test negative but are experiencing symptoms. Additionally, if you have extreme symptoms and are in need of medical attention, don’t rely on a home test – go seek that medical attention. He noted that you shouldn’t rely on a false sense of security with just one test. When you’re testing yourself a few days before you travel, for example, that may not be the most accurate depiction of your health status if you’re going out in public afterward. You should still be careful if you get a negative test result and make sure to follow public health guidelines.
POPSUGAR aims to give you the most accurate and up-to-date information about the coronavirus, but details and recommendations about this pandemic may have changed since publication. For the latest information on COVID-19, please check out resources from the WHO, the CDC, and local public health departments.