Thyrotropin results in euthyroid patients with a past history of hyperthyroidism.

Sensitive TSH levels were measured in 93 euthyroid patients with a past history of hyperthyroidism. Subnormal TSH values were found in 18 out of 75 (24%) patients previously treated with a course of antithyroid drugs, and in 3 out of 18 (17%) post-thyroidectomy patients. These subnormal TSH results are a limitation to the general application of the TSH-first strategy. Twelve months follow-up showed that subnormal TSH values are associated with increased risk of relapse in the antithyroid drug treated group (p less than 0.001). Longer follow-up varies in duration and some late relapses have occurred in drug treated patients with normal baseline TSH levels. To date relapses have occurred in 3 out of 56 normal TSH patients compared with in 6 out of 16 suppressed TSH patients; no thyroidectomy patients have relapsed. Prospective studies are needed to confirm the predictive value of sensitive TSH measurements.