Adding a tonsil specimen to a throat swab does not improve the detection rate of SARS-CoV-2 - a multicenter randomized controlled trial

BACKGROUND: In many jurisdictions, throat swab is the standard specimen for molecular testing for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), and billions of tests have been performed worldwide to date. Despite differing opinions on the diagnostic value of including sample material from the palatine tonsils when performing the throat swab, no studies have investigated the effect on the detection rate of SARS-CoV-2.

METHODS: A randomized controlled trial was conducted in two public test centers for SARS-CoV-2 in Denmark. Participants were invited to participate in the trial due to either symptoms of upper airway infections or screening purposes. The trial took place from November 10 through December 22, 2022. Participants were randomized into two groups in a 1:1 ratio; one group receiving a throat swab of the posterior oropharyngeal wall only and the other group receiving a throat swab of the posterior oropharyngeal wall including the palatine tonsils. All participants filled out a baseline questionnaire, including discomfort with the test. The main outcome was reverse transcription polymerase chain reaction (RT-PCR) test result with a cycle threshold value <38 considered positive and ≥ 38 negative.

RESULTS: Overall, 2,315 participants enrolled in the study. In the control group, 29.2% of 1157 enrolled had a positive SARS-CoV-2 test for COVID-19, while 29.8% of 1158 enrolled in the tonsil group had a positive test (OR 0.97, 95% CI 0.84;1.13). The tonsil group reported a mean discomfort score of 0.27 points higher on a 11-point Numerical Rating Scale compared to the control group (95% CI 0.06;0.49).

CONCLUSIONS: Including the palatine tonsils in throat swabs does not increase the detection rate for SARS-CoV-2, but is associated with more discomfort compared to throat swabs avoiding the palatine tonsils.