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Adding a throat swab specimen to a nasal specimen significantly increased sensitivity of COVID-19 rapid antigen tests, whether self-collected or collected by a healthcare worker, a randomized clinical trial showed.

With combined nasal and throat specimens, sensitivity reached 81.4% for healthcare worker-collected specimens and 73.4% for self-collected specimens, increases of 21.4 and 15.5 percentage points compared with a single nasal specimen alone (both P<0.001), reported Tobias Todsen, MD, PhD, of Copenhagen University Hospital in Denmark, and colleagues.

In addition, healthcare worker-collected throat specimens had higher mean sensitivity than nasal specimens for rapid antigen testing (69.4% vs 60%). "To our knowledge, our study is the first to demonstrate that healthcare worker-collected throat specimens for COVID-19 rapid antigen testing have a significantly higher sensitivity than healthcare worker-collected nasal specimens," the authors wrote in .

"I was surprised to find out that the throat had a significantly better sensitivity than nasal swabs, meaning that billions of rapid antigen tests were performed in a suboptimal way during the pandemic," Todsen told MedPage Today in an email. "Further, I was surprised that the early infectious stages primarily tested positive for throat rather than nasal swabs."

"Our findings contrast with other respiratory viruses that primarily infect the nasal mucosa and may explain the rapid SARS-CoV-2 transmission in the community, as speaking and sneezing generate droplets from the throat," he added.

As for self-collected nasal or throat specimens, there was no significant difference in sensitivity (57.9% vs 53.7%, P=0.17). Self-collection of throat specimens detected fewer positive cases of COVID compared with throat specimens collected by healthcare workers (P<0.001), suggesting that it is more difficult for people to correctly swab their own throats.

In fact, in participants who were symptomatic for COVID, self-collected nasal specimens were actually more sensitive than self-collected throat specimens, with a mean sensitivity of 71.5% versus 58% (P<0.001).

The use of throat swabs for COVID rapid antigen testing is controversial and, to date, studies have reported mixed results. For example, found that self-collected throat specimens performed worse than self-collected nasal swabs, with just 47% of positive COVID cases being detected by throat swabs versus 86% detected by nasal swabs. However, found that a combination of throat and nasal swabs resulted in a positive percent agreement of nearly 82% compared with 68% with nasal swabbing alone.

To date, the any rapid antigen test that uses throat specimens. There may be little incentive to move forward with developing over-the-counter COVID rapid antigen tests that include throat swabbing because the tests would have to be redesigned and evaluated, increasing not only costs to manufacturers, but also the difficulty of self-collecting a sample, Todsen and team noted.

However, they concluded that their "findings suggest that current testing recommendations should include throat specimens to improve the sensitivity of rapid antigen testing. Further research should confirm our findings using redesigned or other rapid antigen testing devices and explore whether throat specimens can also improve the detection of other common airway infections."

This multicenter study included 2,674 participants ages 16 and older with complete test results, of whom 31% were positive for SARS-CoV-2 when tested using reverse transcriptase-polymerase chain reaction (PCR) from throat specimens, nasal specimens, or both. Median age was 40, and 57.4% were women. The majority of participants were vaccinated against COVID-19.

Participants were randomized 1:1 to self-collected or healthcare worker-collected nasal and throat swab specimens for rapid antigen testing. They had a total of four samples collected at one of two outpatient test centers in Copenhagen, and received a handout to instruct them how to perform self-swabbing, as well as a mirror to assist in self-swabbing of the pharynx and tonsils. Samples were sequenced for SARS-CoV-2 variants, and the majority were primarily Omicron BA.2 or BA.2.9.

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