Rates of Detecting Thyroid Nodules Recommended for Biopsy with Ultrasound: Are All Indications Equal?

The use of thyroid ultrasound increases yearly, adding to costs and overdetection of clinically irrelevant nodules. We investigated which indications most commonly prompt referral for thyroid ultrasound and the diagnostic utility by indication. We performed a retrospective observational cohort study of adults (≥18 years) undergoing an initial dedicated thyroid ultrasound between 2017 and 2019 at a tertiary academic center. Indicated reasons for referral were categorized into suspected palpable nodule (SPN), compressive symptoms (CS), metabolic symptoms (MS), screening due to high-risk factors, follow-up of incidental finding on other imaging, and combination of factors. Percentage of ultrasounds with an identifiable nodule and with a nodule recommended for biopsy was compared by indication. Separate logistic regression models were used to identify factors associated with finding any nodule and a biopsy-recommended nodule. Among the 1739 patients included, the most common indication for thyroid ultrasound was SPN (40%), followed by incidental imaging (28%), CS (13%), combination (11%), MS (6%), and high-risk factors (2%). Overall, 62% of ultrasounds identified a nodule. Ultrasounds performed for incidental findings had the highest rate of nodule identification (94%), compared with 55%, 39%, and 43%, for SPN, CS, and MS, respectively (p < 0.05). Only 27% of ultrasounds identified a biopsy-recommended nodule. Nodules found incidentally had the highest rate of biopsy-recommended nodules at 55%. Rates of biopsy-recommended nodules for SPN, CS, and MS were 21%, 6%, and 10%, respectively. Logistic regression demonstrated that compared with patients referred for an SPN, those with incidental nodules were 10 times more likely to have a nodule found on ultrasound (odds ratio [OR] = 10.6 [CI 7.0-16.0]), while those referred for CS were half as likely to have a nodule (OR = 0.5 [CI 0.4-0.7]). Similar factors were associated with identification of biopsy-recommended nodules. Of all new dedicated thyroid ultrasounds, only a quarter find biopsy-recommended nodules, and nearly 40% do not identify a nodule at all. Notably, only 55% of ultrasounds done for SPN found a nodule. Ultrasound for CS and MS had the lowest rates of detecting nodules. Providing clear guidance on when to order thyroid ultrasounds can help reduce unnecessary health care utilization and potential overtreatment.