Combined use of conventional smear and liquid-based preparation versus conventional smear for thyroid fine-needle aspiration

The purpose of the study was to compare the diagnostic utility of the combined conventional smear (CS) and liquid-based preparation (LBP) compared to CS with respect to the non-diagnostic rate, the atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS) rate, and the diagnostic performances for malignancy. This retrospective study was approved by the Institutional Review Board, and the need to obtain informed consent was waived. In our institution, thyroid FNAs were processed with CS before October 2012, and LBP has been used in combination with CS after October 2012. On-site evaluation for the adequacy of CS was not performed. This study included nodules 5 mm or larger with FNAs performed by faculties: 811 nodules in 773 patients for CS, and 926 nodules in 894 patients for combined CS and LBP. Nodules with surgery or either benign or malignancy cytology on initial or repeat FNA were regarded to have the reference standards needed to calculate diagnostic performances. The proportion of Bethesda categories and diagnostic performances were compared between the two groups with z test. The non-diagnostic rate, the AUS or FLUS rate, and the diagnostic performances for malignancy were similar (All P > 0.05). The follicular neoplasm (FN) or suspicious for FN rate decreased from 1.2 to 0.3 % (P = 0.034). The benign rate increased from 51.4 to 57.0 % (P = 0.019). Combined CS and LBP decreased FN or suspicious for FN diagnoses, and increased benign diagnoses compared to CS with comparable non-diagnostic rates and AUS or FLUS rates, and comparable diagnostic performances.