The Ideastream Health Team is working to answer listeners’ questions about COVID-19, with help from local experts. You can send us your questions with our online form, through our social media group, or call us at 216-916-6476. We'll keep the answers coming on our website and on the air.
Rowan in Shaker Heights recently tested positive for COVID-19 after receiving a negative test result a few days earlier. He asked, “How can testing best be used to avoid false negatives? Does being vaccinated make you more likely to get a false negative from either kind of test?”
There are several potential reasons for false-negative test results, said Dr. Christine Schmotzer, vice chair of system pathology at University Hospitals.
One of the biggest is timing, she said. A person may test negative if there is not enough virus present in the sample, which can happen in the early days after contracting the virus, she said.
Once a person is feeling symptoms, they are recommended to get tested, Schmotzer said.
“Even if you have symptoms and you have a negative test, maybe there just wasn’t enough virus there at the time,” Schmotzer said. “We do advise that if people have a negative test and symptoms, that again, they talk to their doctor … and they may have them retest in another 1 to 2 days.”
Another factor in the accuracy of a COVID-19 test is the type of test, she said. PCR tests – which are conducted and analyzed through a hospital or lab – are more accurate than rapid at-home antigen tests, like the kind people purchase in drug stores, she said.
“PCR will become positive with lower amounts of virus present,” Schmotzer said. “The PCR testing will have a lower [risk of] false negative than the rapid antigen testing.”
Rapid tests are still helpful in showing whether someone has COVID-19 at a given time, and they are most accurate when the person is symptomatic, she added.
Another common reason for a false negative is individual error, Schmotzer said. A person may have not gotten a good enough sample on the nasal swab - so she recommends reading the directions of at-home rapid tests carefully, she said.
“You have to do a really good quality swab,” Schmotzer said. “The swab needs to be far up enough in your nose as to be uncomfortable.”
When it comes to COVID-19 testing, the guidance depends on the situation, she added. If an individual is showing COVID-19 symptoms, they are typically advised to test as soon as possible, she said.
If the person came into close contact with someone who tested positive for COVID-19, the testing recommendations vary depending on whether they are vaccinated, she added.
If the individual is unvaccinated, they are recommended to get a COVID-19 test right away, but if they are fully vaccinated, they can take a test within 5 to 7 days after exposure for peace of mind, she added.
The listener also asked if being vaccinated makes people more likely to get a false negative. There is a slight chance of this occurring, Schmotzer said, because research shows they do not shed as much of the virus as those who are unvaccinated.
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