Background: Fine-needle aspiration (FNA) plays a pivotal role in the initial evaluation of patients with thyroid nodules. Traditionally, aspirated material is expelled directly onto the microscope slide to make a conventional smear (CS). Recently, liquid-based preparations (LBP) have gained in popularity. This study compares the accuracy of these two preparation techniques in diagnosing thyroid nodules.
Methods: A clinical database containing 5475 thyroid cytology consults from 2009 to 2013 was queried to identify 5169 CS and 306 LBP cases. Cytological diagnostic frequency rendered before and after second review were compared between LBP and CS. Correlation with the histology diagnosis was also calculated for each preparatory technique.
Results: Age, sex, and nodule size were comparable between patients who had FNA processed by LBP and CS. More LBP cases than CS cases were inadequate (17% vs. 10%; p<0.001). LBP cases had fewer benign diagnoses (39% vs. 47%; p=0.003) and tended to have more malignant diagnoses (16% vs. 12%; p=0.09) when compared to CS. Indeterminate and suspicious categories were comparable between LBP and CS. Correlation with histology was also comparable between both techniques.
Conclusion: LBP was associated with a significantly higher proportion of inadequate and a lower proportion of benign diagnoses. Thus, universal adoption of LBP may introduce more inadequate samples. Future investigations should explore the lack of on-site evaluation with LBP as a potential source for the high inadequate rate.