Suppression of Thyrotropin (H-TSH) in Serums of Patients with Myxedema of Varying Etiology Treated with Thyroid Hormones

Abstract

Patients with myxedema and high thyrotropin (h-TSH) levels were given levothyroxine (l-T₄) orally in doses increasing stepwise from 0.025 to 0.2 mg per day at 3-week intervals. The serum h-TSH response was similar regardless of etiology of the myxedema. In all but one patient, h-TSH levels were suppressed to normal at 0.2 mg per day, but at lower doses, many patients still had increased h-TSH levels when total and free T₄ levels were normal. h-TSH was correlated with dose of T₄ (r equals -0.99), total T₄ (r equals -0.99), and free T₄ (r equals -1.0). Five patients were given levo-tri-iodothyronine (l-T₃) orally in doses increasing each week by 25 μg daily to 100 μg per day; serum h-TSH levels became normal in all patients with 100 μg per day but not with 75 μg per day. For T₃ suppression tests, 75 μg per day is not sufficient for routine use. Serum h-TSH levels appear to offer the best means of diagnosing hypothyroidism and assessing adequacy of thyroid-hormone therapy.