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People walk past COVID-19 testing booths in Manhattan on March 30, 2022. (Hiroko Masuike/The New York Times)
(Science Times)
What does a negative result on a home test for COVID-19 really mean?
That’s the question that baffles many people who have resorted to a home test because of a sore throat, cough or runny nose. After passing a swab through the nose and waiting an agonizing 15 minutes, the result is negative.
Although a negative result is a relief, it also makes us feel uncertain. Am I really free from COVID-19? Or rather the test did not detect it? Should I get tested once more? Can I be with other people?
According to testing and public health experts, the confusion is justified. It is due to a lack of understanding of how the tests work. Rapid home antigen tests look for viral protein fragments from a swab from your nose and are designed to identify if you have an infectious level of the virus. However, a negative test does not guarantee that you do not have COVID-19.
Your symptoms may be an immune response signaling the arrival of COVID-19 or another invader. The harder your immune system works to curb the virus, especially if it’s boosted by antibodies in the vaccine, the more likely you are to get an early negative result on a rapid test, even if you’re infected.
“It might be that the virus in your body is fighting a battle once morest your immune system,” explained Michael Mina, chief scientific officer of eMed, a company that helps users of rapid tests receive treatment from home. “If the test is negative and you have symptoms, don’t assume it’s negative. It assumes that the virus has not yet had a chance to develop. The symptoms may mean that your immune system is only giving very early warning.”
Mina advises people to get a rapid test on the first day of symptom onset. A positive result means that you almost certainly have COVID-19. If the result is negative and the symptoms continue, take precautions, wear a face mask and avoid close contact with other people. If you can’t test every day, wait 48 hours and repeat the test. If the result is still negative, but the symptoms persist or worsen, you should take another test on the fourth day. You can also go to a testing center for a PCR test, which can sometimes detect COVID-19 a little earlier than a home test, although you may have to wait a day or two for the results.
Experts say that if you have symptoms and home test results are still negative, it may be that your immune system is doing a good job of beating the virus. Or you may have another disease. In any case, avoid infecting others.
“If you have symptoms and the tests are still negative, the chances that you can spread the disease are lower,” says Robert Wachter, chairman of the Department of Medicine at the University of California, San Francisco. “But chances are that day you have to wear a mask because you have something.”
And remember, the result of your home test is just a fact. If you haven’t left the house in weeks, your negative result following a few tests may be accurate. If you have symptoms and have been to bars or a member of your family has been exposed to COVID-19, you should be more cautious, even if the initial results are negative. It might be that you were tested too early and your viral load is not high enough to be detected.
When Jillian Horton, an internist from Winnipeg, Manitoba, started feeling ill, she was pretty sure she had COVID-19. Her husband had been exposed and also had symptoms. She decided to carry out an experiment, she was tested several times over the course of a few days to follow the dynamics of the virus. “Because my husband tested positive and I had a lot of symptoms, I was sure he had COVID-19,” Horton said. “I was curious to see if you might pinpoint when he might test positive.”
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People receive free COVID-19 test kits at the American Museum of Natural History in Manhattan on March 30, 2022. (Hiroko Masuike/The New York Times)
Horton’s husband started showing symptoms on a Friday night and that night her test was negative. On Saturday, she began to feel unwell and took the test three times throughout the day. All three results were negative.
On Sunday morning he woke up and felt worse. At 6 a.m. he took the test and he saw a faint line, which he called a “weak positive.” Two more tests were done on Sunday and both were negative.
On Monday morning, he was tested once more and promptly came back positive.
The remarkable thing regarding Horton’s experiment is that if he had tested at a different time on Sunday, he might never have discovered the weak positive. It was evident that his immune system was fighting the virus, as evidenced by the two negative results he obtained that same day.
Horton noted that getting tested at the right time to catch a high viral load is like putting a net across a stream. If there are no fish, you will not catch anything. But if you set the net at the time when the fish are plentiful, you will have fish for dinner.
Horton said he’s concerned that too many people think tests don’t work when, in fact, they’re a useful tool if you know how to use them. They are ideal for “ruling out” the presence of COVID-19, but more information must be taken into account when evaluating a negative test.
“I often hear people say, ‘The test is useless,’” says Horton. “What my experience illustrates is that when you have symptoms, the tests are really ‘rule out’ tests. I think back to those two days when I had so many symptoms. One test was positive and five were negative. There was only one moment when I was more contagious.”
Mina says that despite the limitations, people can benefit from frequent testing whenever they suspect they’ve been exposed, have symptoms, or want to make sure they’re not infectious before interacting with a high-risk person. She also recommends getting tested before you see other people once more to make sure you can’t spread it to them.
“These are tools that have enormous benefit during a pandemic like this. They will tell you when you are most likely to spread the disease,” Mina said. “Most of the time they will tell you at what point you are barely infectious. They will identify almost everyone who has a viral load high enough to be contagious. But they won’t be perfect.”
