Thyroglobulin in Lymph Node Aspirate

Abstract

Lymph node involvement in patients with differentiated thyroid cancer is an important finding and typically requires further therapy beyond thyroidectomy. While fine-needle aspiration cytology has been considered the gold standard for diagnosis, studies on resected lymph nodes have shown a high rate of false-negative results. Measurement of thyroglobulin in washout fluid from the needle used for aspiration cytology has shown an increased ability to recognize nodal involvement by thyroid cancer. Most studies have used 0.5 mL of saline to wash out the needle, although larger amounts of saline and different fluids have also been used without a discernible difference in diagnostic performance, although matrix effects should be explored. Plain tubes should be used to collect fluid, since false-negative results have been rarely observed with other collection tubes. Since immunometric assays have been used, the possibility of high-dose hook effect causing falsely low results should be evaluated, but has not been to date. Thyroglobulin levels over 1 μg/L (ng/mL) have most commonly been used as the cutoff for considering results indicative of nodal involvement, although there is no consensus on the best cutoff value, and some data suggest that higher cutoff values should be used in lymph node aspirates from patients who have not yet undergone thyroidectomy. The presence of thyroglobulin or heterophile antibodies in serum does not seem to affect results, although this has not been extensively evaluated, and at least two cases with false-negative results revealed after recombinant TSH stimulation have been reported. Diagnostic performance overall typically shows sensitivities and specificities well over 95 %.