Inconclusive cytology results of fine-needle aspiration for thyroid nodules: the importance of strict guideline implementation.

Purpose: This study investigated whether strict adherence to the Korean Thyroid Imaging Reporting and Data System (K-TIRADS) biopsy indications could reduce inconclusive cytology results and evaluated associated clinical factors.

Methods: This retrospective study included 2,440 nodules from 2,256 patients who underwent initial fine-needle aspiration (FNA) for thyroid nodules from January to December 2022. Inconclusive specimens were defined as Bethesda categories I and III, while conclusive specimens comprised Bethesda categories II, IV, V, and VI. Nodules smaller than the K-TIRADS biopsy threshold were considered FNA not-indicated nodules. Clinical factors included patient age, sex, ultrasound features, nodule size, number of needle passes, and operator experience. Univariate and multivariate logistic regression analyses were performed to assess the associations between clinical factors and inconclusive results.

Results: Among 2,440 nodules, 900 yielded initial inconclusive biopsy results, while 1,540 provided conclusive results. Independent predictors of inconclusive biopsy results included FNA not-indicated nodules, nodules sized 0 to 5 mm, operator experience of less than 1 year, older age, and K-TIRADS category 4 (P<0.001, P=0.006, P=0.003, P=0.001, and P<0.001, respectively). Among K-TIRADS category 4 nodules, the presence of suspicious ultrasound characteristics was negatively associated with inconclusive biopsy results (P=0.004).

Conclusion: FNA not-indicated nodules, nodule size of 0 to 5 mm, operator experience of less than 1 year, older age, and K-TIRADS category 4 were factors associated with inconclusive biopsy results. Strict adherence to the K-TIRADS biopsy indications may reduce inconclusive cytology results.