When you should use a home COVID-19 test
When is a home test for COVID-19 the right test?
When you don’t have access or the time for a test administered by a professional, and you understand the limitations of home tests, says William Agel, MD, MPH, chief medical officer for Cape Cod Healthcare.
“They need to be used for generalized peace of mind, but they can’t be relied upon,” he said. “The most important thing: If you have symptoms and your [home] test is negative, it does not mean you don’t have COVID. It means you need to get tested by a professional with a standard polymerase chain reaction (PCR) test.”
Home tests are sold at pharmacies and online, although they have been in short supply. The White House announced Oct. 6 that President Biden was scaling up production of home COVID tests and hoped to make them more readily available by December. That should help consumers get a quick read on questionable symptoms or take a test when they can’t get to a COVID testing center.
Home tests can be confusing, however, and there are things to understand to make them more reliable. And, be aware that some places or travel destinations requiring a negative COVID test may not accept results from a self-test. Here is Dr. Agel’s advice on how to use them properly.
What are the types of COVID tests?
The “gold standard” and most sensitive test for the SARS-CoV-2 virus that causes COVID-19 is the RT-PCR test. It picks up minute amounts of the viral genetic material RNA and amplifies it to the point it can be detected, according to Dr. Agel. These tests, offered at medical centers and testing sites, require a swab high into your nose or nasopharynx. The sample is then sent to a laboratory, and you get results in a few days.
“That’s the most sensitive test and it’s maybe as much as 98 percent sensitive in patients in whom it’s done correctly,” he said.
Doctors’ offices or urgent care centers might also offer a nucleic acid amplification (NAT) test that produces results in about 15 minutes. “It’s similar to a PCR but not quite as sensitive, so it will have some false negatives,” Dr. Agel said.
One type of home COVID test is also a PCR test, using a swab that you take yourself and send off to a laboratory. Results take several days. These tests cost about $100 to $125 at pharmacies.
The other home test is an antigen test that detects the proteins that coat the virus, Dr. Agel said. The swab then is mixed with a reagent that produces a color indicator in a way similar to a home pregnancy test. Results are available in about 15 minutes and the tests are less expensive -- about $23.
“The problem with antigen tests like the in-home tests is that they are less sensitive than the PCR or NAT tests,” Dr. Agel said. “In a patient who’s really symptomatic, they’ll pick up three out of four people who have COVID, generally speaking.”
How do I know if a home COVID test is appropriate?
The antigen tests are useful if you have suspicious symptoms and can’t get to a testing center, Dr. Agel said.
“You test and it’s positive, you’ve got COVID,” he said. “If it’s negative, you’d still need a PCR test and would probably need to go to a testing center. If you just want some reassurance - perhaps if you think you were exposed a few days ago and you want to do a home test - that’s fine. But if it’s negative, it’s not a guarantee you don’t have COVID.”
How can I make a home test more reliable?
Make sure you take the swab according to the manufacturer’s instructions, Dr. Agel said.
“For a PCR test, the nasopharyngeal swab, where they get further back into the [nose openings], are the most sensitive. As you come further and further out the nose, it becomes less sensitive because there’s less replicating virus there. It’s similarly so with the antigen test….But the key is to follow the instructions on the home kits to the letter.”
Will my vaccination status affect my home test?
“The vaccines don’t interfere with any of the testing other than antibody testing to see if you have antibodies. But those aren’t generally done. Neither the PCR or antigen tests are interfered with by previous vaccination,” he said.
What should I do if my home COVID test is positive?
First, quarantine or isolate yourself. Second, call your doctor, Dr. Agel said.
“Contact your physician because there are treatments available for people who are at higher risk for progression to severe disease. In most cases, if you’re a young and healthy person without comorbidities, you just isolate for the appropriate amount of time. At this point it’s usually 10 days after first symptoms, but your doctor and public health authorities can help you with that.”