Background: The 2016 American Thyroid Association guidelines recommend that hyperthyroid patients should be euthyroid before thyroidectomy. This recommendation is based on low-quality evidence. In this retrospective cohort study, we compare peri- and post-operative outcomes of patients with hyperthyroidism who were controlled versus uncontrolled at the time of thyroidectomy. Methods: A retrospective cohort study was performed on 275 hyperthyroidism patients at a single institution from December 2015 to November 2022. Patients were defined as hyperthyroid if they had a diagnosis of hyperthyroidism with at least one suppressed thyrotropin (TSH). Patients were considered uncontrolled if triiodothyronine or thyroxine (T4) was elevated immediately before surgery. Patient demographics, perioperative data, and postoperative outcomes were compared with Chi-square and Wilcoxon Rank Sum tests, as appropriate. Results: Of the 275 patients, 84.3% were women and 51.3% were uncontrolled at time of surgery. Controlled patients had higher median [interquartile range] TSH (0.4 [0.0, 2.4] mIU/L vs. 0.0 [0.0, 0.0] mIU/L, p < 0.001) and lower free T4 (fT4) (0.9 [0.7, 1.1] ng/dL vs. 3.1 [1.9, 4.4] ng/dL, p < 0.001), respectively. Uncontrolled patients were more likely to be diagnosed with Grave's disease (85.1% vs. 67.9%, p < 0.001) and to undergo surgery due to medication intolerance (12.1% vs. 6%) or history of thyroid storm (6.4% vs. 1.5%) (p = 0.008). Uncontrolled patients were also more likely to take a larger number of preoperative medications (2.3 vs. 1.4, p < 0.001). No patient in either group experienced thyroid storm precipitated by surgery. Controlled patients had shorter operative times (7.3% vs. 19.8% <1 hour, p < 0.014) and decreased median estimated blood loss (15.0 [5.0, 30.0] mL vs. 20.0 [10.0, 50.0] mL, p = 0.002). Both groups experienced similar, low rates of postoperative complications, apart from an increase in temporary hypocalcemia in the uncontrolled group (13.4% vs. 4.7%, p = 0.013). Conclusion: Our study is the largest to date examining the postoperative outcomes of patients with uncontrolled hyperthyroidism who undergo thyroidectomy. Our results affirm that thyroidectomy in actively thyrotoxic patients is safe and will not precipitate thyroid storm.

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