Impact of Operator Specialization and on‐Site Evaluation on Nondiagnostic Thyroid Fine‐Needle Aspiration: A Comparative Study

BACKGROUND: Thyroid fine-needle aspiration (FNA) is the primary diagnostic method for evaluating thyroid nodules; however, nondiagnostic results remain a significant limitation, often leading to repeat procedures and delayed diagnosis. Operator specialization and rapid on-site evaluation (ROSE) have been proposed as strategies to improve specimen adequacy. METHODS: This retrospective comparative study included all thyroid FNA procedures performed in 2025 at the University Clinical Center of Kosovo (UCCK), where procedures were performed by endocrinologists and radiologists without routine rapid on-site evaluation (ROSE), and at the Hospital for Tumors, UHC "Sisters of Charity", Zagreb, where procedures were performed by interventional cytopathologists with routine ROSE implementation. Cytology results were classified according to The Bethesda System for Reporting Thyroid Cytopathology. The proportion of nondiagnostic results between institutions was compared using the chi-square test. RESULTS: A total of 2171 thyroid FNA procedures were analyzed (1728 at UCCK and 443 at Hospital for Tumors). The nondiagnostic rate was significantly higher at UCCK (182/1728; 10.5%) compared with Hospital for Tumors (11/443; 2.5%) (p < 0.0001), corresponding to an odds ratio of 4.62 (95% CI, 2.50-8.54). Repeat FNA was performed in 36.3% of nondiagnostic cases at UCCK, of which 81.8% yielded a diagnostic Bethesda category. CONCLUSION: A significantly lower rate of nondiagnostic thyroid FNA results was observed in the center with interventional cytologists and routine ROSE implementation. These findings support the role of operator specialization and on-site adequacy assessment in improving specimen adequacy and reducing the need for repeat procedures.