FNA-Tg improves the diagnostic efficacy of FNAC for PTC lateral cervical LN metastasis

The detection of thyroglobulin in lymph node (LN) fine needle aspirates (FNA-Tg) is an effective supplement to ultrasound and fine needle aspiration cytology (FNAC) in diagnosis of cervical LN metastases for patients with papillary thyroid carcinoma (PTC). However, there is no unique cutoff value of FNA-Tg in practice. We aimed to determine the optimal cutoff of FNA-Tg and evaluate the interfering factors of FNA-Tg. A serial of 405 lateral cervical LN samples from 317 patients with PTC were analyzed retrospectively. Receiver operating characteristic (ROC) curve was used to determine the optimal cutoff of FNA-Tg. The factors that impact FNA-Tg were evaluated. Serum Tg, serum thyroglobulin antibody (TgAb) and serum thyroid stimulating hormone (TSH) level, and thyroid status did not differ between the malignant and benign LN groups. The median FNA-Tg was 3.81 ng/mL (0.16–33.40 ng/mL) in LNs without metastasis and 310.32 ng/mL (124.41–500.00 ng/mL) in LNs with metastasis, and the differences reached statistical significance (P < 0.01). The optimal cutoff of FNA-Tg was 36.22 ng/mL, and the values of area under the curve (AUC), sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) was 0.88, 0.89, 0.75, 0.91 and 0.71, respectively. The diagnostic accuracy of FNA-Tg cutoff of 36.22ng/mL was 85%. When FNAC and the present FNA-Tg cutoff of 36.22 ng/mL were combined together, the diagnostic sensitivity, specificity, PPV, NPV and diagnostic accuracy was 0.96, 0.75, 0.92, 0.87 and 91%, respectively. FNA-Tg improves the diagnostic efficacy of FNAC for PTC lateral cervical LN metastasis, and the optimal cutoff value of FNA-Tg was 36.22 ng/mL. FNA-Tg was affected by LN status but was not associated with serum Tg, serum TgAb, serum TSH and thyroid status.