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Influence of Human Body Composition on Serum Peak Thyrotropin (TSH) after Recombinant Human TSH Administration in Patients with Differentiated Thyroid Carcinoma

Department of Endocrinology and Metabolism (M.G.C., A.P., A.M., M.G., E.M., P.F., L.G., F.S., R.E.), University of Pisa, 56100 Pisa, Italy; Department of Internal Medicine, Endocrinology and Metabolism, and Biochemistry (F.P.), University of Siena, 53100 Siena, Italy; and AmbiSEN Center, High Technology Center for the Study of the Environmental Damage of the Endocrine and Nervous Systems (A.P.), University of Pisa, 56124 Pisa, Italy

Address correspondence and requests for reprints to: R. Elisei, M.D., Department of Endocrinology, University of Pisa, Via Paradisa 2, 56124 Pisa, Italy. E-mail: relisei{at}endoc.med.unipi.it.

Objectives: In this study, we evaluated the influence of height, weight, body mass index (BMI), body surface area, and body composition [total lean body mass (LBM) and fat body mass] on serum peak TSH levels obtained after recombinant human (rh)TSH. Furthermore, to verify whether the serum peak TSH influenced the efficacy of radioiodine (¹³¹I), we compared the rate of thyroid remnant ablation according to the patients’ BMI.

Patients: We studied 105 patients with differentiated thyroid carcinoma who underwent rhTSH stimulation test. Serum TSH measurements were performed before and 24, 48, and 72 h after rhTSH administration. We also compared the rate of thyroid remnant ablation among 70 differentiated thyroid carcinoma patients with different BMI.

Results: The serum peak TSH after rhTSH was significantly lower in overweight and obese subjects compared with normal-weight subjects (92.1 ± 41.8, 82.4 ± 24.2, and 112.7 ± 46.3 µU/ml, respectively; P = 0.01) and in males compared with females (74.6 ± 22.3 and 105.0 ± 43.0 µU/ml, respectively; P = 0.0002). By univariate analysis, serum peak TSH was negatively related to weight, height, body surface area, BMI, LBM, and fat body mass, but only LBM was independently associated with serum peak TSH levels. Although it was confirmed that overweight and obese patients had a lower serum peak TSH, the rate of ablation did not differ among normal-weight, overweight, and obese patients.

Conclusions: With this study we demonstrated that LBM is the only parameter independently associated with serum peak TSH after rhTSH administration. However, the serum peak TSH does not influence the rate of ¹³¹I remnant ablation.