RESUMEN
BACKGROUND: The use of thyroglobulin concentration in washout fluid of fine-needle aspiration (FNA-Tg) is a procedure advocated by international guidelines to diagnose metastatic LN in papillary thyroid cancer. With the increasing use of active follow-up or lobectomy alone for low-risk thyroid cancers, the determination of the diagnostic performance of FNA-Tg in the detection of metastatic PTC when the thyroid is in situ is paramount. MATERIALS AND METHODS: Prospective study with measurement of Tg in washout fluid obtained from intraoperative fine needle aspiration (FNA) cytology in order to avoid contamination from thyroid tissue and rigorously isolated punctured nodes. Receiver-operating characteristic (ROC) curve and area under the curve (AUC), optimal threshold to discriminate benign and malignant LN, sensitivity and specificity were provided. RESULTS: a total of 58 lymph nodes from 32 patients were analyzed. ROC analysis defined the optimal cutoff values of FNA-Tg at 60 ng/ml for the diagnosis of malignant LNs in patients with a thyroid in situ. Sensitivity and specificity were 75% (95% confidence interval 57.89-86.75) and 87.5% (95%CI: 69-95.66), respectively. CONCLUSION: Our results support the hypothesis that the Tg-FNA threshold for a safe diagnosis of LN metastasis in PTC is higher in presence of a thyroid gland in situ. The use of lower thresholds could result in false positive results and lead to unnecessary surgery.