High Serum Thyrotropin Concentrations within the Reference Range: A Predictor of Malignancy in Nodular Thyroid Disease

Objective: This study assessed whether or not a simple biochemical parameter, serum thyrotropin (TSH), within the reference range can predict the likelihood of thyroid malignancy in subjects undergoing fine-needle aspiration biopsy (FNAB) for thyroid nodules. Subjects and Methods: This cross-sectional study evaluated 236 patients without overt thyroid dysfunction who were not on levothyroxine therapy. They underwent FNAB of the thyroid nodules at the Clementino Fraga Filho University Hospital between 2011 and 2012. The reference range and serum TSH quartiles were determined according to age-specific values for serum TSH and then compared between the cases with benign thyroid nodular disease and differentiated thyroid carcinoma (DTC) based on surgical pathology reports. Results: Of the 236 patients, 201 (85.1%) underwent a surgical procedure (thyroidectomy) and 89/236 (44.3%) had DTC. The mean TSH concentrations were 2.09 ± 1.15 mU/L in benign patients versus 2.73 ± 1.33 mU/L in cases of DTC ( p < 0.01). As TSH increased from quartiles 1 to 4, the frequency of a malignant diagnosis also increased progressively from 22% in quartile 1 to 65% in the last quartile ( p ≤ 0.001). Conclusion: Thyrotropin levels were positively associated with the diagnosis of DTC in thyroid nodules.