Background: Processing methods for fine-needle aspiration biopsy (FNA) samples mainly include conventional smears (CS) and liquid-based preparations (LBP). There is still debate as to which method is better and the diagnostic value and necessity of combining the two methods remains unclear. The objective of the current study was to compare the diagnostic performance of the two methods and their combined use in thyroid nodules.
Methods: We analyzed thyroid cytopathology data from 16 medical centers between June 2010 and November 2025, comparing nondiagnostic and indeterminate nodules rates across preparation methods. For histologically confirmed samples, diagnostic performance metrics were calculated. Cases with separate CS and LBP descriptions (multi-diagnoses group) were analyzed for diagnostic consistency and performance.
Results: In total, 89,392 thyroid FNA cases were included (49,309 CS, 13,161 LBP, and 26,922 combined). The rate of indeterminate nodules was 10.3% (CS), 10.9% (LBP), and 14.8% (combined), while nondiagnostic rate was lowest in the combined group (7.3% vs. 10.5% for CS and 17.9% for LBP). LBP demonstrated higher sensitivity (98.1% vs. 95.0%) and accuracy (97.0% vs. 93.7%) than CS, while combined use provided no significant advantage over LBP alone. In the multi-diagnoses group, CS-LBP concordance among diagnostic samples was 92.9%, with comparable diagnostic performance across all methods.
Conclusions: LBP demonstrated superior diagnostic performance compared with CS, but combined use of both methods provided no significant advantage over LBP alone.
Keywords: conventional smears; diagnostic performance; fine-needle aspiration; liquid-based preparations; thyroid cytopathology.