• Xinyan Cai, Mark H Ebell, and Garth Russo.
• From Department of Epidemiology and Biostatistics, College of Public Health, University of Georgia, Athens, GA(XC, MHE); University of Georgia Health Science Center, Athens, GA (GR).
• J Am Board Fam Med. 2022 Dec 23; 35 (6): 106510711065-1071.

BackgroundOrdering a serologic test for infectious mononucleosis (IM) in all young patients with sore throat is costly and impractical. The test threshold to determine when to order a diagnostic test for IM based on the patient's symptoms has not been previously studied.ObjectiveTo determine the test threshold for IM in the management of patients with sore throat.Design And SettingOnline surveys were sent to a convenience sample of US primary care clinicians regarding their decision making about whether or not to order a test for IM in a patient with sore throat.Method7 clinical vignettes were created, each with a different combinations of symptoms and signs. The probability of IM for each vignette was estimated by the investigator based on the number of symptoms present to generate a plausible range of disease probabilities. Clinicians were then asked to decide whether to test or not test for IM, and mixed-effect logistic regression was used to determine the test threshold for IM where half of physicians chose to test and half chose not to test.ResultsA total of 117 clinicians provided responses for a total of 819 clinical vignettes. The overall test threshold for IM as estimated using the logistic regression was 9.5% (95% CI: 8.2% to 10.9%). The test threshold for clinicians practicing greater than 10 years was significantly higher than for those practicing less or equal to 10 years (10.5% vs 7.3%, P = .02). No significant differences between specialties and practice sites were found with respect to the test threshold.ConclusionThis study identified a test threshold for IM of approximately 10% based on realistic clinical vignettes. This threshold was stable regarding the clinician's specialty and practice sites and could be used in the development of a clinical prediction rule to determine the cutoff for low- versus high-risk groups.© Copyright by the American Board of Family Medicine.

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