Normal Serum Concentrations of Sex Hormone Binding-Globulin in Patients with Hyperthyroidism due to Subacute Thyroiditis

Serum concentrations of sex hormone binding-globulin (SHBG) were determined in patients with hyperthyroidism (n = 94; 12 men, 82 women) due to either Graves' disease (n = 59; 11 men, 48 women), autonomous thyroid adenomas (n = 23; 1 man, 22 women), or subacute thyroiditis (n = 12; all women). Elevated serum concentrations of SHBG were initially seen in 57 of 82 patients (69%) with hyperthyroidism due to either Graves's disease or due to autonomous adenoma. Elevated serum SHBG concentration was more frequent in patients with serum total thyroxine (TT₄) concentrations greater than 15.0 μg/dL (32/39 [82%]; including 3 patients with autonomous adenoma) compared to those with serum TT₄ concentration between 11.0 and 15.0 μg/dL (21/27 [77%]; including 7 patients with autonomous adenoma), or patients with an isolated elevation of serum total triiodothyronine (TT₃) concentration (4/16 [25%]; including 2 patients with autonomous adenoma). Serum SHBG concentration normalized when patients became euthyroid. Only 1 of 12 patients in the hyperthyroid phase of subacute thyroiditis had an elevated serum concentration of SHBG. Serum concentrations of thyroid binding globulin (TBG) and transcortin (CBG) were normal in all but 1 patient. In patients with hyperthyroidism as a result of Graves' disease or autonomous adenoma serum SHBG concentrations were elevated with the greatest elevation found in patients with the highest serum T₄ concentrations. The normal concentrations of SHBG in the hyperthyroid phase of subacute thyroiditis most likely reflects the shorter duration of exposure to increased thyroid hormone in this condition.