Screening for Subclinical Thyroid Dysfunction in Non-Pregnant Adults: A Summary of the Evidence

The term subclinical hyperthyroidism describes conditions characterized by a low thyroid-stimulating hormone (TSH) and normal levels of circulating thyroid hormones (thyroxine and triiodothyronine). Subclinical hyperthyroidism has the same causes as overt hyperthyroidism. These include excessive doses of levothyroxine, Graves’ disease, multinodular goiter, and solitary thyroid nodule. Most studies of the course of subclinical hyperthyroidism concern patients whose history, physical examination, ultrasound, or thyroid scan suggests one of these causes. There are relatively few studies of patients who are found by screening to have an undetectable TSH, normal free thyroxine (FT4) and normal free triiodothyronine (FT3) levels, and a negative thyroid evaluation, the largest group identified in a screening program. The prevalence of subclinical hyperthyroidism is about 1% (95% confidence interval [CI], 0.4%–1.7%) in men older than 60 and 1.5% (CI, 0.8%–2.5%) in women older than 60.