Evaluation of Thyroid Function

The lifetime prevalence of thyroid dysfunction, hypothyroidism, and hyperthyroidism is about 10% in North America. Thyroid disease occurs in women 2 to 3 times more commonly than men. Thyroid dysfunction may have a variable clinical presentation depending on the age of the patient, degree of dysfunction, and the duration of disease. Thus, its clinical diagnosis is often challenging. Fortunately, the presence of thyroid dysfunction can be easily confirmed biochemically. The clinical picture, together with the judicious use of a limited number of biochemical testing and imaging modalities, can be used to diagnose most of the thyroid illnesses encountered by primary care and family practice physicians, obstetricians, and gynecologists. This chapter will review the basics of thyroid testing, including imaging of the thyroid gland, and will develop a straightforward approach to the diagnosis of hypothyroidism and hyperthyroidism.