Hemithyroidectomy Eligibility Under ATA 2015 and 2025 Criteria: A Reclassification Cohort Study

To compare hemithyroidectomy eligibility and completion thyroidectomy recommendations under the ATA 2015 and ATA 2025 criteria within the same patient cohort (primary aim) and, as a secondary descriptive analysis, to assess the concordance between these guideline-based classifications and the operations actually performed.

Retrospective cohort study of adult patients who underwent primary hemithyroidectomy for differentiated thyroid carcinoma at a tertiary center (January 2015-November 2025). NIFTP and tumors of uncertain malignant potential were excluded from the comparative analysis. Each case was independently reclassified by ATA 2015 and ATA 2025 criteria using final histopathology (a retrospective, hindsight reclassification that could not have informed preoperative decisions); paired comparisons used the McNemar test.

Of 98 patients, 86 were eligible for comparative analysis. Hemithyroidectomy eligibility increased from 60.5% (52/86) under ATA 2015 to 81.4% (70/86) under ATA 2025 (absolute increase 20.9 points; 95% CI 12.3-29.5; p < 0.001). Completion thyroidectomy indications decreased from 44.2% (38/86) to 29.1% (25/86) (absolute reduction 15.1 points; 95% CI 7.5-22.7; p < 0.001). Despite this reduction, completion was actually performed in 40.7% (35/86) of the comparative cohort (vs. 35.7% overall; the difference reflects exclusion of NIFTP and tumors of uncertain malignant potential).

The ATA 2025 criteria substantially expand hemithyroidectomy eligibility and reduce completion thyroidectomy indications compared with ATA 2015. Real-world completion rates nonetheless exceeded guideline-based projections, suggesting that additional pathological and clinical factors may influence individualized surgical decision-making. These findings characterize the guideline update's impact on surgical strategy and do not address long-term oncologic outcomes, which were beyond this study's scope.