January 11, 2022 – Many Americans are familiar with rapid antigen tests for COVID-19 that include a nasal swab. But some new evidence points to a saliva the sample could increase the accuracy of the tests.
Experts agree on one thing: if you plan to test both nose and throat, wipe your throat first.
As for the official position, the FDA says follow the testing instructions. In other words, hold on to your nose for now.
“We don’t have enough data to suggest that throat swabs are an accurate or appropriate method for home tests,” the agency wrote on January 7 on Twitter.
One leading infectious disease physician may disagree.
Robert Wachter, MD, shared a story on Twitter about how his symptomatic son was initially negative using a quick nasal swab test. After searching for additional tests, sampling of both throat and nose gave a positive result.
“I tweeted about Covid for almost 2 years. But this week it became personal when my 28-year-old younger son got it. With his permission, I will describe his experience and how I approached his situation, given the realities of life and the evidence that they are changing fast, ”he wrote on Twitter on January 8th.
Wachter is chairman of internal medicine at the University of California, San Francisco and a contributor to Medscape Medical News., WebMD’s sister site for medical professionals.
Preprints support saliva sampling
Two recent preprint studies support a strategy of taking a saliva swab. The warning with preprints is that the research has not been reviewed yet.
The researchers compared the accuracy of saliva and nasal sampling to 382 people with symptoms who also underwent PCR tests.
Rapid saliva test results were consistent in 100% of cases with a standard laboratory PCR test for the presence of the Omicron variant, Marais and colleagues from Cape Town University and the National Health Laboratory Service in South Africa reported.
In contrast, the results of nasal rapid tests agree in 86% of the time.
The results, the authors say, may mean we need to rethink typical diagnostic testing for suspected COVID-19 cases.
Saliva seems more accurate
Saliva sampling and throat swabs are not necessarily the same thing, says Christina Wojewoda, MD, chair of the College of American Pathologists’ Committee on Microbiology.
For example, in one of the new studies, participants received the following instructions:
“Participants were not supposed to eat, drink, tobacco or gum in 30 minutes before taking a saliva swab. Participants were initially instructed to cough 3-5 times, covering their mouths internally elbow. They were then asked to wipe the inside of both cheeks, above and below language, on the gums and hard palate. A minimum smear duration of 30 seconds was required. “
This technique makes more sense than directly clearing the throat, she said. “Getting a well-collected throat swab on myself … would be hard. I’d shut my mouth and spit.”
More research is needed to determine the best way to collect saliva, says Wojewoda, who is also the director of the Clinical Microbiology Laboratory at the University of Vermont Medical Center.
“We know from the rapids strep by examining studies that show that accurate collection of samples from the back of the throat is not easy, ”says Michael Blaivas, MD, chief medical officer at Anavasi Diagnostics.
This means that clinical expertise can make a big difference in sample collection. A throat swab done by a doctor, nurse or other healthcare professional in general will always be more accurate than one done by someone less familiar with proper technique, he said.
Rapid tests may need to be reconsidered
Anavasi Diagnostics has a quick molecular test based on wiping the lower nose that can give results in 30 minutes.
“This Marais study studied salivary and secondary PCR[nostril] PCR. This is very different from salivary antigen tests, “Blaivas said.
“However, if others confirm the findings of the study and it is true that Omicron causes a greater secretion of the virus in the mouth or saliva than in the nose, companies will have to consider redesigning their tests,” he said.
Another warning about a quick nose test?
Researchers have reported differently preprint study comparing the effect of saliva-based PCR tests with those of nasal rapid antigen tests in 30 people who tested positive as part of a screening program.
Blythe Adamson, Ph.D., and colleagues reported that most people with Omicron tested positive for PCR days before antigen tests gave the same result.
“This study sounds reasonable to me,” Wojewoda says. “We know that PCR will always be more sensitive than an antigen test.”
“So I think this really limits the use of antigen tests to ‘Oh, wow, I feel awful today. Let me get an antigen test, and if it’s positive, I consider myself positive. If it’s negative, I could still be positive.’ and I will need to do a PCR test. ‘”
In contrast, for asymptomatic coronavirus patients, it looked as if the antigen tests were “pretty bad,” Wojewoda says.
The Adamson study also confirms the widespread belief that “rapid antigen tests are often not sensitive enough to diagnose infection when the wound is or the symptoms are mild and when little virus is excreted,” Blaivas said.
“My clinical experience in the emergency department has shown regularly, early on pandemic, that antigen tests were not reliable for our clinical use, “Blaivas said.” We accidentally admitted more patients to non-COVID wards when they were actually COVID-positive … because the hospital ran out of internal PCR tests. during a repeated wave of infections. “
Blaivas recommended consulting with regularly updated FDA website which lists antigen tests that fail to reliably identify the Omicron variant.
The best of both worlds?
Some experts support taking throat and nose swabs, “and there is literature that this is more accurate than just a throat swab,” Blaivas said.
But, he says, “some tests will fail if they face a sample from the nose or throat if they are not prepared and tested on it.”