Can liquid-based preparation substitute for conventional smear in thyroid fine-needle aspiration? A systematic review based on meta-analysis

OBJECTIVE: Conventional smear (CS) using fine-needle aspiration cytology (FNAC) has been established as the test of choice for diagnosing thyroid lesions, despite low sample adequacy and inter-individual variations. Although a liquid-based preparation (LBP) technique has been recently applied to overcome these limitations, its clinical utility and its accuracy over CS are controversial. This study aimed to determine the true sensitivity and specificity of LBP in thyroid FNAC by meta-analysis. DESIGN: Systematic review with meta-analysis. METHODS: We searched major electronic databases (MEDLINE, EMBASE, Cochrane library, Google Scholar) with queries of ‘thyroid’, ‘LBP’ and ‘liquid-based cytology’. Original articles including cytohistologic correlation data comparing the accuracy of any LBP technique, such as ThinPrep, SurePath and Liqui-Prep, with CS were included for qualitative meta-analysis and preparation of synthesized reporter-operating curves (sROC). RESULTS: A total of 372 studies were screened and 51 original articles were eligible for full-text review; finally, 24 studies were chosen for the meta-analysis. Average sample inadequacy was significantly lower in two mainstream LBP methods (ThinPrep and SurePath) than CS. Specificity and sensitivity by sROC were similar or slightly superior for LBP vs CS. Various cytomorphologic changes by each method have been reported. CONCLUSIONS: Although a learning curve is essential for adapting to the cytomorphologic features of the LBP technique, our results support the use of two mainstream LBPs alone in thyroid FNAC that LBP will increase the sample adequacy and reduce the workload with similar accuracy. More data and further evaluation are needed for the other LBP methods.