The utility of thyroglobulin washout studies in predicting cervical lymph node metastases: One academic medical center's experience.

BACKGROUND: Fine-needle aspiration cytology (FNAC) is useful for evaluating cervical lymph nodes for metastases from thyroid carcinomas. Reports have illustrated that with application of standardized technique and appropriate cutoffs, thyroglobulin (TG) washout studies increase the sensitivity and specificity of FNAC in identifying lymph node metastases. This project describes our experience at an academic medical center utilizing needle wash thyroglobulin analyses as an ancillary to FNAC.

MATERIALS AND METHODS: We reviewed cases at our institution where thyroglobulin analysis was performed in conjunction with FNA of lymph nodes in patients with thyroid carcinoma. Thyroglobulin levels were measured on needle rinses from each FNA biopsy that appeared negative or equivocal at the time of immediate assessment. These results were compared with surgical pathology results from neck dissections, when performed.

RESULTS: 168 FNA biopsies were performed on suspicious lymph nodes from 97 patients with known or suspected thyroid malignancy between April 2013 and present. Using a cutoff of 1.0 ng TG/ml, thyroglobulin studies performed at our institution were found to have sensitivity and specificity results of 0.95. Surgical pathology results were used as the gold standard. When surgical pathology results are not available, FNAC is used as the mode of comparison. False positive Tg results occurred in two prethyroidectomy patients suggesting that sample contamination with blood may influence this method's specificity. A false-negative Tg result occurred in a lymph node with <1 mm focus of metastatic PTC, indicating that Tg results may not be sensitive in cases with few tumor cells.

CONCLUSIONS: Our results suggest that thyroglobulin washout studies improve the quality of our biopsy diagnoses when used in conjunction with FNA in the assessment of metastatic disease in the context of established thyroid malignancy in post-thyroidectomy patients. Thyroglobulin values close to the cutoff of 1.0 ng/ml should be interpreted with caution, as these may represent a minute focus of metastatic tumor. Tg values in prethyroidectomy patients should also be interpreted with caution, as contamination with blood may cause its elevation. Diagn. Cytopathol. 2016;44:964-968. © 2016 Wiley Periodicals, Inc.