Comparison of the diagnostic value of thyroglobulin measurement in needle washouts by FNAC and by FNCC for detecting node metastases in thyroid papillary carcinoma

Objective: To compare the value of thyroglobulin(Tg) measurement by fine needle aspiration and by fine needle capillary techniques for diagnosing node metastases from thyroid papillary carcinoma(PTC). Methods: Fifty-four patients with suspicious metastatic lymph nodes from PTC were enrolled during January 2018 to December 2018. Ultrasound guided fine needle aspiration cytology(FNAC) and fine needle capillary cytology(FNCC) were performed for detecting suspicious lymph nodes, and the level of Tg in the eluent was measured. According to the post-operative pathologic results and clinical follow-up results, the difference of diagnostic efficacy between the two groups was compared. Results: A total of 76 suspicious lymph nodes were examined, and 48 of them were confirmed as metastasis by pathology. The mean level of Tg in needle washouts by FNAC and by FNCC were （4 588.02±1 042.09） ng/mL and (1 678.57±420.57) ng/mL (P=0.010 6), respectively. The area under receiver operating characteristic curve of Tg value in washouts by FNAC and by FNCC were 0.943 and 0.913, respectively. The difference was significant between methods (P=0.032). The cut-off value of Tg in FNAC group was 14.385 ng/mL, and the diagnostic sensitivity and specificity were 0.938 and 0.893, respectively. The cut-off value of Tg in FNCC group was 12.155 ng/mL, and the diagnostic sensitivity and specificity were 0.875 and 0.893, respectively. Conclusions: Both measurement of Tg in the eluent by FNCC and by FNAC are helpful to the diagnosis of metastatic lymph nodes from PTC. However, FNAC had more advantage over FNCC in diagnosing metastatic lymph nodes.