Evolution of thyroid fine-needle aspiration biopsy performance over 15 years: implications for risk stratification in clinical practice.

OBJECTIVE: We aimed to evaluate temporal changes in the diagnostic performance of thyroid fine-needle aspiration biopsy (FNAB) over a 15-year period in a single-center, surgically confirmed cohort. SUBJECTS AND METHODS: We retrospectively analyzed thyroid FNABs performed between 2009 and 2023, dividing the data into two intervals (Group 1: 2009-2014; Group 2: 2015-2023). All specimens were interpreted by the same two experienced cytopathologists. Sensitivity, specificity, and Youden's J were calculated at four diagnostic thresholds (≥AUS/FLUS, ≥FN/SFN, ≥SM, and malignant only), and level-specific likelihood ratios (LRs) were compared between cohorts. Overall diagnostic discrimination was assessed with receiver operating characteristic (ROC) curves and compared by DeLong's test. RESULTS: The study included 1,241 nodules; after excluding non-diagnostic cytology, 601 nodules in Group 1 and 553 in Group 2 were available for diagnostic performance analysis. At the ≥AUS/FLUS cutoff, sensitivity increased from 85.6% to 94.8%, while specificity declined from 58.4% to 33.0% (both p<0.01). Specificity at higher thresholds remained similar or increased in Group 2. The area under the ROC curve (AUC) was 0.799 for Group 1 and 0.831 for Group 2 (p = 0.24). Of the five Bethesda LRs, only that for AUS/FLUS changed significantly (1.24 vs. 0.37; p<0.01). CONCLUSION: The overall discriminative ability of the Bethesda System remained stable over 15 years. The decrease in the AUS/FLUS LR reflects a spectrum effect driven by more selective surgical referral patterns and should be interpreted as a change in cohort composition rather than diminished test performance.