Which COVID-19 test should you get?
Some tests look for the DNA of the virus, others look to see if your body is waging a war against the virus and therefore producing antigens. One takes time, the other is rapid. And doctors say speed isn’t always the most sound choice.
Dr Karen Kaul is a pathologist at NorthShore University HealthSystem.
“We do have a need for rapid, easily administered tests in this country as we try to go about our daily business,” she said.
There is value in a rapid test for large events or medical procedures when there is a need to know immediately.
But speed sacrifices accuracy.
“The rapid tests in general tend to be less sensitive,” Kaul said. “As is the case with any type of COVID testing, it’s important to be cautious, wear masks and continue to social distance because it’s possible to get a false negative result as we are seeing in this country.”
Abbott insists its antigen screen identifies positive test results 95-percent of the time and renders a negative result in 97.9-percent of samples.
But doctors in the heart of COVID units treating patients say in their experience, the rapid, 30 minute tests, made by multiple manufacturers, are only 70% sensitive in accurately identifying SARS CoV-2, the virus that causes COVID-19. And when patients are tested too early when viral levels are low, it may give a false negative.
“It’s impossible to recognize that a test is a snapshot in time of that patient,” Kaul said. “And we have had patients who tested negative who were symptomatic and were retested some days later and became positive. We just had caught them too early on the first sampling of that patient.”
Walking around with a false sense of security may lead some to unknowingly spread COVID-19. And it is important to seek out testing if exposed to this coronavirus. Multiple testing options make that easier. Some places are doing what seems to be more comfortable testing as opposed to the deep nasal approach. But the risks may outweigh the benefits.
“The gold standard test is still going to be a deep nasal swab,” Kaul said. “A nasal pharyngeal swab followed up by PCR testing – that is the best specificity and sensitivity we can offer anywhere in the world. However it’s difficult to administer those swabs. It’s less comfortable for patients. So many locations are now doing less deep or anterior swabs. The sensitivity is a little less because we’re not collecting as much virus on those types of samples as you would get from a nasal pharyngeal swab.”
Throat swabs are also now available.
“Similarly there’s been a lot in the news lately about saliva testing and saliva is a sample we can use by whatever analytical means we have in the lab,” Kaul said. “It is a little less sensitive most likely, but easier to collect and doesn’t need medical professional in PPE. But the trade off is perhaps a little bit of sensitivity in detecting the virus. … In the hospital setting the last thing we wanted was someone coming in with an unexpected COVID that could spread it around the hospital. So we’ve been very cautious in the hospital setting to use the most sensitive test possible.”
The bottom line is if a person wants to do what the medical professionals do for testing, go with the deep nasal swab PCR test.