Subclinical Hypothyroidism

Abstract Subclinical hypothyroidism is a common condition associated with a raised serum thyroid-stimulating hormone (TSH) but normal serum free thyroxine and triiodothyronine. It is more prevalent in women and people with advancing age. Most patients with subclinical hypothyroidism are asymptomatic. About 2.5% patients progress to overt hypothyroidism annually although the rate of progression is higher in the presence of thyroid autoantibodies. Subclinical hypothyroidism is associated with an increased risk of coronary heart disease, heart failure and cerebrovascular disease in younger patients (<65 years), particularly in those with TSH ≥10.0 mU/L. Currently, there is no randomized controlled trial evidence that levothyroxine prevents these complications, although a large observational study has shown that levothyroxine may reduce the risk of coronary heart disease in younger patients (<70 years). The treatment decision for subclinical hypothyroidism requires careful consideration of the patients’ age as well as the presence of symptoms, thyroid autoantibodies, and cardiovascular risk factors.