A swab from the nose, throat, or both for quick tests on COVID-19?

January 11, 2022 – Many Americans are aware of rapid antigen tests for COVID-19, which include nasal swabs. But some new evidence suggests that a saliva sample could increase test accuracy.

Experts agree on one thing: If you are going to test your nose and throat, get a throat swab first.

As for the official position, the FDA says the test guidelines should be followed. In other words, stick to your nose for now.

“We do not have enough data to suggest that throat swabs are an accurate or appropriate method for home tests,” the agency wrote on Twitter on January 7.

One leading infectious physician might disagree.

Robert Wachter, MD, shared on Twitter the story of how his symptomatic son was first tested negative using a quick nasal swab test. After searching for further tests, sampling of the throat and nose yielded 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 reality of life and the rapidly changing evidence. , “He wrote on Twitter on January 8.

Wachter is the President of Internal Medicine at the University of California, San Francisco and a contributor to Medscape Medical News, WebMD is a sister site for medical professionals.

Preprints support saliva sampling

Two recent prepress studies support a saliva swab strategy. The prepress warning is that the research has not yet been reviewed.

One study by Gert Marais, MD, and colleagues says that the use of saliva to detect coronavirus infections is better than a nasal swab.

The researchers compared the accuracy of saliva and nasal sampling in 382 people with symptoms, who also had PCR tests done.

The results of a rapid saliva test were 100% consistent with a standard laboratory PCR test for the presence of the Omicron variant, said Marais and colleagues at the University of Cape Town and the National Health Laboratory Service in South Africa.

In contrast, the results of the rapid nasal test agreed in 86% of cases.

The results, the authors say, may mean that we need to reconsider the typical diagnostic tests performed for suspected COVID-19.

Saliva looks more accurate

Saliva sampling and throat swabs are not necessarily the same, 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 should not have any food, drink, tobacco or chewing gum within 30 minutes prior to saliva collection. Participants were initially instructed to cough 3-5 times and cover their mouths with their inner elbow. They were then asked to wipe inside both faces, above and below “The swab lasted at least 30 seconds.”

This technique makes more sense than direct throat swabs, she said. “Getting a well-picked throat swab … would be hard. I’d gag and spit.”

More research is needed to “find” the best way to collect saliva, says Wojewoda, who is also the director of the Laboratory of Clinical Microbiology at the University of Vermont Medical Center.

“We know from rapid streptococcal testing that accurate sampling of the back of the neck is not easy,” said Michael Blaivas, MD, chief physician at Anavasi Diagnostics.

This means that clinical expertise can make a big difference in sampling. A throat swab made by a doctor, nurse or other health care professional in general will always be more accurate than one performed by someone less familiar with the proper technique, he said.

Quick tests may need to be reconsidered

Anavasi Diagnostics has a rapid molecular test based on a lower nose swab that can return results within 30 minutes.

“This Marais study focused on saliva PCR and secondary[nostril] PCR. This is very different from saliva antigen testing, “said Blaivas.

“However, if the findings and conclusions of the study confirm others and it is true that Omicron causes higher excretion of viruses in the mouth or saliva than in the nose, companies will have to consider reworking their tests,” he said.

Another warning about a quick nose test?

The researchers published another prepress study that compared the performance of saliva-based PCR tests with the results of nasal rapid antigen tests in 30 people who tested positive in a screening program.

Blythe Adamson, PhD, and colleagues reported that most people with Omicron tested positive by PCR days before antigen testing yielded the same result.

“I find this study reasonable,” says Wojewoda. “We know that PCR will always be more sensitive than the antigen test.”

“So I think that really limits the use of antigen tests to ‘Oh, gentlemen, I feel miserable today. Let me do an antigen test, and if it’s positive, I consider myself positive. If it’s negative, I can still be positive.’ I’ll have to do a PCR test. ‘”

In contrast, in asymptomatic patients with coronavirus, the antigen tests seemed to “perform quite poorly,” says Wojewoda.

Adamson’s study also confirms the widespread belief that “rapid antigen tests are often not sensitive enough to diagnose infection when it is early or when symptoms are mild and low in virus,” said Blaivas.

“My clinical experience in the emergency room regularly showed, at the beginning of the pandemic, that antigen testing was not reliable for our clinical use,” Blaivas said. “We mistakenly admitted several patients to the ward without COVID when they were in fact COVID positive … because the hospital ran out of internal PCR tests during a recurring wave of infections.”

Mr Blaivas recommended consulting the FDA’s regularly updated website, which lists tests for antigens that do not reliably detect Omicron.

The best of both worlds?

Some experts support throat and nose swabs, “and there is support in the literature to be more accurate than throat swabs themselves,” Blaivas said.

But he says: “Some tests fail if they are confronted with a sample from the nose or throat, if they are not adapted and tested for it.”

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