Factors Influencing the Sample Adequacy of Ultrasound-Guided Fine-Needle Aspiration from Solid Thyroid Nodules for Liquid-Based Cytology: A Demographic, Sonographic, and Technical Perspective

Background and Objectives: To identify factors that influence the sample adequacy of solid thyroid nodules based on ultrasound-guided fine-needle aspiration (FNA) with subsequent liquid-based cytology. Materials and Methods: We retrospectively reviewed 855 patients who underwent ultrasound-guided FNA at our hospital between July 2019 and July 2020. The final analysis included 801 solid thyroid nodules in 801 patients. After reviewing the demographic data, ultrasonic features, and FNA technique-related factors, we defined 14 potential variables. For cytological results, the Bethesda categories II–VI were defined as adequate sample results. Univariate and multivariate analyses were performed to identify factors that influenced sample adequacy. Results: The adequate sample rate was 87.1%. The univariate analysis showed that four factors were related to adequate sampling in patients with thyroid FNA. These factors included age (p < 0.001), nodule orientation (p = 0.0232), calcification (p = 0.0034), and operator experience (p = 0.0286). After the multivariate analysis, five independent factors were identified to improve the diagnostic results of FNA for solid thyroid nodules: (1) the presence of Hashimoto’s thyroiditis (odds ratio (OR) = 1.810; 95% confidence interval (CI): 1.076–3.045; p = 0.0254), (2) a taller-than-wide orientation (OR = 2.038; 95% CI: 1.260–3.296; p = 0.0037), (3) the presence of calcification (OR = 1.767; 95% CI: 1.115–2.799; p = 0.0153), (4) four needle passes to obtain material (OR = 1.750; 95% CI: 1.094–2.799; p = 0.0196), and (5) an experienced operator (OR = 0.561; 95% CI: 0.319–0.987; p = 0.0451). Conclusions: A taller-than-wide orientation, the presence of calcification, and the presence of Hashimoto’s thyroiditis were found to affect the sample adequacy of ultrasound-guided FNA with liquid-based cytology. The sample adequacy could be improved when FNA is performed with four needle passes by experienced doctors.