Subclinical Hypothyroidism


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Abstract

KEY CLINICAL POINTSSubclinical HypothyroidismSubclinical hypothyroidism is defined as an elevated thyrotropin level with a normal free thyroxine (T4) level. To confirm the diagnosis, a transient increase in thyrotropin should be ruled out by a repeat measurement of thyrotropin and free T4 after 2 to 3 months.In up to 46% of patients with subclinical hypothyroidism who have a thyrotropin level of less than 7 mIU per liter, the thyrotropin level normalizes within 2 years.Subclinical hypothyroidism, particularly when the thyrotropin level is more than 10 mIU per liter, is associated with an increased risk of hypothyroid symptoms and cardiovascular events.There are few data from randomized, controlled trials of levothyroxine therapy for subclinical hypothyroidism to inform the effects of treatment on cardiovascular outcomes.Treatment is generally recommended for persons 70 years of age or younger who have thyrotropin levels of at least 10 mIU per liter, although long-term benefits have not been shown.Among patients who have thyrotropin levels of less than 10 mIU per liter or who are older than 70 years of age, treatment decisions are based on individual patient factors (e.g., symptoms of hypothyroidism, a positive test for antibodies to thyroid peroxidase, or cardiac risk factors).

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