Serum thyroglobulin, high-resolution ultrasound, and lymph node thyroglobulin in diagnosis of differentiated thyroid carcinoma nodal metastases.

Abstract

Clinically enlarged cervical lymph nodes in patients with a history of thyroid cancer are usually assessed by fine-needle aspiration biopsy (FNAB) followed by cytology with or without tissue core. Thyroglobulin (Tg) is frequently elevated in malignant FNAB needle-wash specimens and may possibly augment or replace cytology. Furthermore, the combination of undetectable serum Tg and an innocuous ultrasound might altogether obviate the need for biopsy. The objectives of the study were to: 1) determine an appropriate diagnostic cutoff for Tg levels in FNAB; 2) assess the diagnostic performance at this cutoff; and 3) compare serum Tg and FNAB needle-wash Tg levels to determine whether serum Tg levels predict positive Tg FNAB. This was a retrospective study of 122 FNAB samples in 88 athyrotic thyroid cancer patients. Fifty of 52 nonmalignant FNAB samples (96.2%) had Tg 1 ng/ml or less. All 70 malignant FNAB had Tg greater than 1 ng/ml. Of 103 specimens with diagnostic cytology, five (4.9%) had discordant Tg results; in four of these FNAB Tg was concordant with the final diagnosis. Eighteen of 19 (94.7%) FNAB with nondiagnostic (n = 16) or absent (n = 3) cytology were correctly classified by FNAB needle-wash Tg. Undetectable (<0.1 ng/ml) serum Tg was associated with a negative diagnosis in 21 of 23 biopsies (91.7%); the two cancer-positive samples were both serum Tg autoantibody positive and classified as suspicious by ultrasonography. Nodal FNAB needle-wash Tg measurements complement cytology in thyroid cancer follow-up and might substitute for it. The combination of unremarkable ultrasonography and an undetectable serum Tg in Tg autoantibody-negative patients might obviate the need for FNAB.