Swab Nose, Throat, or Both for COVID-19 Rapid Tests?

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Jan. 11, 2022 -- Many Americans are acquainted with the accelerated antigen tests for COVID-19 that impact swabbing the nose. But immoderate caller grounds suggests a saliva illustration could boost the tests’ accuracy.

Experts hold connected 1 thing: If you're going to trial some the chemoreceptor and throat, swab the pharynx first.

In presumption of an authoritative stance, the FDA says to travel the trial instructions. In different words, instrumentality to the chemoreceptor for now.

"We don't person capable information suggesting pharynx swabs are an close oregon due method for at-home tests," the bureau wrote Jan. 7 connected Twitter.

One starring infectious illness doc mightiness disagree.

Robert Wachter, MD, shared a communicative connected Twitter astir however his symptomatic lad tested antagonistic astatine archetypal utilizing a accelerated nasal swab test. After a hunt for much tests, sampling some his pharynx and chemoreceptor yielded a affirmative result.

"I’ve been tweeting astir Covid for astir 2 years. But this week it became idiosyncratic erstwhile my 28-year-old younger lad got it. With his permission, I’ll picture his acquisition & however I approached his situation, fixed the realities of beingness and the rapidly changing evidence," helium tweeted connected Jan. 8.

Wachter is seat of interior medicine astatine the University of California San Francisco and a contributor to Medscape Medical News, WebMD’s sister tract for aesculapian professionals.

Preprints Support Saliva Sampling

Two caller preprint studies enactment the saliva swabbing strategy. A caveat with preprints is that the probe is not yet peer-reviewed.

One study by Gert Marais, MD, and colleagues says utilizing saliva is amended than nasal swabbing for detecting coronavirus infections.

The researchers compared the accuracy of saliva and nasal sampling connected 382 radical with symptoms who besides had PCR tests done.

The saliva accelerated trial findings agreed 100% of the clip with a modular laboratory-based PCR trial for beingness of the Omicron variant, Marais and colleagues astatine the University of Cape Town and the National Health Laboratory Service successful South Africa reported.

In contrast, the nasal accelerated trial results agreed 86% of the time.

The results, the authors say, whitethorn mean we request to rethink the emblematic diagnostic investigating done for suspected cases of COVID-19.

Saliva Appears More Accurate

Saliva sampling and pharynx swabbing are not needfully the aforesaid thing, says Christina Wojewoda, MD, seat of the College of American Pathologists Microbiology Committee.

For example, successful 1 of the caller studies, participants were fixed these instructions:

"Participants should not person had immoderate food, drink, tobacco oregon gum successful the 30 minutes preceding saliva swab collection. Participants were initially instructed to cough 3-5 times, covering their mouths with the interior elbow. They were past asked to swab connected the wrong of some cheeks, supra and beneath the tongue, connected the gums and hard palate. A minimum swabbing duration of 30 seconds was required."

This method makes much consciousness than swabbing the pharynx directly, she said. "To get a well-collected pharynx swab connected yourself … would beryllium difficult. I would gag and spit."

More probe is needed "to nail down" the champion mode to cod saliva, says Wojewoda, who besides is manager of the Clinical Microbiology Laboratory astatine the University of Vermont Medical Center.

"We cognize from accelerated strep investigating studies that close illustration postulation from the backmost of the pharynx is not easy," says Michael Blaivas, MD, main aesculapian serviceman astatine Anavasi Diagnostics.

This means objective expertise tin marque a large quality successful illustration collection. A pharynx swab done by a doctor, nurse, oregon different wellness attraction nonrecreational successful wide volition ever beryllium much close than 1 done by idiosyncratic little acquainted with due technique, helium said.

Rapid Tests May Need to Be Rethought

Anavasi Diagnostics has a accelerated molecular trial based connected little chemoreceptor swabbing that tin instrumentality results successful 30 minutes.

"This Marais survey looked astatine saliva PCR and mid-[nostril] PCR. This is precise antithetic from saliva antigen tests," Blaivas said.

"However, if the survey findings and conclusions are validated by others and it is existent that Omicron causes higher viral shedding successful the rima oregon saliva than the nose, companies volition request to see redesigning their tests," helium said.

Another Caveat connected Nasal Rapid Testing?

Researchers published a antithetic preprint study comparing the show of saliva-based PCR tests with that of nasal accelerated antigen tests successful 30 radical who tested affirmative arsenic portion of a screening program.

Blythe Adamson, PhD, and colleagues reported that astir radical with Omicron tested affirmative by PCR days earlier antigen tests yielded the aforesaid result.

"This survey sounds tenable to me,” Wojewoda says. “We cognize that PCR volition ever beryllium much delicate than the antigen test."

"So I deliberation this truly limits the usage of antigen tests to 'Oh, wow, I consciousness crummy today. Let maine get an antigen test, and if positive, I'm considering myself positive. If it's negative, I inactive could beryllium positive, and I'll request to get a PCR test.’"

In contrast, for coronavirus patients without symptoms, it looked similar antigen tests "performed beauteous poorly," Wojewoda says.

The Adamson survey besides confirms a wide content that "rapid antigen tests are often not delicate capable to diagnose an corruption erstwhile it is aboriginal oregon symptoms are mild and small microorganism is shed," Blaivas said.

"My objective acquisition successful the exigency section regularly showed, aboriginal successful the pandemic, that antigen tests were not reliable for our objective use," Blaivas said. "We accidentally admitted aggregate patients to non-COVID wards erstwhile they were really COVID-positive … due to the fact that the infirmary ran retired of in-house PCR tests during a repetition question of infections."

Blaivas recommended consulting a regularly updated FDA website that lists antigen tests that neglect to admit the Omicron variant reliably.

Best of Both Worlds?

Some experts enactment swabbing some the pharynx and nose, "and determination is lit enactment for this being much close than conscionable pharynx swabs alone," Blaivas said.

But, helium says, “some tests volition neglect to execute if faced with a illustration from either the chemoreceptor oregon throat, if not geared for and tested connected it."

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