Subclinical thyroid dysfunction.

Subclinical thyroid dysfunction may be defined as an abnormal serum thyrotropin concentration in an asymptomatic patient with a normal serum free thyroxine concentration. This article addresses the prevalence, natural history, and potential pathophysiological consequences of subclinical hypothyroidism and subclinical thyrotoxicosis. Subclinical hypothyroidism, which occurs in more than 10% of women older than 60 years, may be accompanied by an unfavorable serum lipid profile and may lower the threshold for the development of major depressive disorder. Subclinical thyrotoxicosis, which is most commonly due to thyrotropin-suppressive levothyroxine sodium therapy, may be associated with reduced bone mineral density in postmenopausal women and confers a 3-fold relative risk for the development of atrial fibrillation. While there are no outcome data to support therapeutic intervention in subclinical thyroid dysfunction, some screening and management recommendations are offered.