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A Single Recombinant Human Thyrotropin-Stimulated Serum Thyroglobulin Measurement Predicts Differentiated Thyroid Carcinoma Metastases Three to Five Years Later

Divisions of Endocrinology, Diabetes and Metabolism, and Nuclear Medicine and Thyroid Cancer Unit (R.T.K.) and Department of Medicine (E.L.M.), The Ohio State University, Columbus, Ohio 43210; and Division of Medicine (E.L.M.), University of Florida, Shands Hospital, Gainesville, Florida 32610

Address all correspondence and requests for reprints to: Dr. Mazzaferri, Professor of Medicine, Division of Endocrinology, Shands Hospital, 1600 SW Archer Road, P.O. Box 100226, Gainesville, Florida 32610-0226. E-mail: mazz01{at}bellsouth.net.

Context: Testing for residual differentiated thyroid carcinoma relies heavily upon recombinant human (rh)TSH-stimulated serum thyroglobulin (Tg) levels, but the positive predictive value is often low.

Objective: Our objective was to determine the accuracy of a single rhTSH-Tg measurement over time.

Design and Setting: We conducted a prospective follow-up study at the University referral center.

Patients: A total of 107 differentiated thyroid carcinoma patients were stratified according to their initial rhTSH-Tg as follows: group 1 with Tg less than 0.5 (n = 68), group 2 with Tg of 0.6–2.0 (n = 19), and group 3 with Tg greater than 2 ng/ml (n = 20).

Intervention: Clinical evaluations were conducted over 0.9–5.2 yr as follows: Tg during thyroid hormone suppression (n = 27), after rhTSH (n = 59), and/or after thyroid hormone withdrawal (n = 15).

Main Outcome: Tumor was identified in one patient in each of groups 1 (1.6%) and 2 (5.5%), and 16 in group 3 (80%), comprising 19 tumor locations: 11 locoregional, two mediastinal, five lung, and one brain. Tumor was found in 81% with an initial or follow-up rhTSH-Tg greater than 2 ng/ml. TSH-stimulated Tg fell spontaneously to less than 0.5 ng/ml in 50% of group 2 and 5% of group 3 over 1.7–5.0 yr. The positive predictive value of the initial rhTSH-Tg greater than 2 ng/ml was 80%, and the negative predictive value was 98%. After retreatment, 100% of group 1, 74% of group 2, and 55% of group 3 had no evidence of tumor (P = 0.0001).

Conclusions: 1) A single rhTSH-Tg greater than 2 ng/ml predicts persistent tumor, although no value entirely excludes future recurrence. 2) Repeated TSH-stimulated studies are appropriate for patients at risk of recurrence, especially those with an rhTSH-Tg greater than 1 ng/ml. 3) A single rhTSH-Tg less than 0.5 ng/ml without Tg antibody has an approximately 98% likelihood of identifying patients completely free of tumor, a large group in which TSH suppression to less than 0.1 mIU/liter and frequent imaging and TSH-stimulated Tg testing are unnecessary.

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