Screening for thyroid dysfunction. A systematic review 1 included 33 screening studies and 23 controlled studies of treatment for subclinical hypothyroidism or subclinical hyperthyroidism. The yield of screening is highest for women older than 50 years of age. Among all women older than 60 years of age, office-based screening detected 14 cases of over hypothyroidism or hyperthyroidism per 1000 women, or 1 case per 71 women (95% CI 59 to 111 women) screened.
Treating subclinical hyperthyroidism. Because no randomised trial of antithyroid treatment in asymptomatic persons have been done, the effect of early treatment in preventing atrial fibrillation or bone fracture in the future is not known.
Treating subclinical hypothyroidism. Results of three small trials on symptom relief are inconsistent. Early treatment is most likely to be effective in patients who have a markedly elevated TSH level (>= 10mU/L). On the basis of randomised trials, 1 in 8.3 of these women (1 in 519 screened) may benefit from thyroxine therapy given to relieve symptoms. By 5 years, treatment would prevent overt hypothyroidism in 1 of 2 patients, or in 1 or 112 screened. Treatment may reduce the cholesterol level by an average of 8% in patients who have a TSH level of 10mU/L or more and an elevated serum cholesterol level.
Un updated version of the review 2 concludes: The prevalence of unsuspected thyroid disease is lowest in men and highest in older women. Evidence regarding the efficacy of treatment in patients found by screening to have subclinical thyroid dysfunction is inconclusive. Several small, randomized trials of treatment for subclinical hypothyroidism have been done, but the results are inconclusive except in patients who have a history of treatment for Graves' disease, a subgroup that is not a target of screening in the general population. No trials of treatment for subclinical hyperthyroidism have been done. Data on the adverse effects of broader use of levothyroxine is sparse.
An Evidence Review for the U.S. Preventive Services Task Force 3 on the benefits and harms of screening and treatment of subclinical and undiagnosed overt hypothyroidism and hyperthyroidism in adults without goiter or thyroid nodules concluded that screening can identify patients with subclinical thyroid dysfunction or undiagnosed overt thyroid disease, but direct evidence on benefits and harms of screening versus no screening remains unavailable. No study directly assessed benefits and harms of screening versus no screening.
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