Endogenous serum TSH levels and metastatic survey scans in thyroid cancer patients using triiodothyronine withdrawal.

Using a triiodothyronine withdrawal method to produce a hypothyroid state in 38 patients with prior thyroidectomies for differentiated thyroid cancer, 56 H-TSH and T4 levels were measured prior to metastatic survey scans performed with 131I. All the T4 levels were below normal and 55 of the 56 H-TSH levels were elevated. No qualitative differences could be observed in the eight patients who had scans performed after bovine TSH injections and later after triiodothyronine withdrawal. Triiodothyronine withdrawal does induce high endogenous TSH levels and under normal circumstances bovine TSH injections are not required for metastatic scans in patients with thyroid cancer.