Subclinical hypothyroidism and hyperthyroidism are diagnoses based on laboratory evaluation with few if any clinical signs or symptoms. Subclinical hypothyroidism is defined as an elevation in serum thyroid-stimulating hormone (TSH) above the upper limit of the reference range (0.45-4.5 mIU/L) with normal serum FT4 concentration; subclinical hyperthyroidism is defined as a decrease in serum TSH below the reference range with normal serum FT 4 and T3 concentrations. Though these conditions represent the earliest stages of thyroid dysfunction, the benefits of detecting and treating subclinical thyroid disease are not well established. Most persons found to have subclinical thyroid disease will have TSH values between 0.1 and 0.45 mIU/L or between 4.5 and 10 mIU/L, for which the benefits of treatment are not clearly established; treatment may be beneficial in individuals with serum TSH lower than 0.1 mIU/L or higher than 10 mIU/L. This article illustrates approaches to managing patients with subclinical hypothyroidism and hyperthyroidism through 5 case scenarios that apply the principles of evidence-based medicine. Because of the substantial uncertainty concerning the consequences of untreated subclinical hypothyroidism and hyperthyroidism, as well as the benefit of initiating treatment, patient preferences are important in deciding on management of subclinical disease.
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