1. According to a review from the U.S. Preventive Services Task Force (USPSTF), more research is needed to determine clinical the benefits of thyroid screening.
Evidence Rating Level: 2 (Good)
Study Rundown: In 2004, the USPSTF found insufficient evidence to recommend for or against thyroid screening in asymptomatic, non-pregnant adults, but rates of thyroid medication prescription in the U.S. have increased more than 40% between 2006 and 2010. This report was commissioned to build on previous reviews on subclinical thyroid disease, and it differs from past publications by addressing identification and treatment of undiagnosed overt thyroid disease. From this review, no direct evidence on the effects of thyroid screening versus no screening on clinical outcomes was identified. Treatment of subclinical hypothyroidism was not associated with benefit in quality of life, cognitive function, blood pressure, bone density, or body mass index. One fair-quality retrospective cohort study found treatment of subclinical hypothyroidism associated with decreased risk for cardiac events, cancer, and all-cause mortality, however it was observational and with methodological limitations. Additionally, while treatment of subclinical hypothyroidism may have some beneficial effects on total cholesterol and LDL, findings were of uncertain clinical significance or lacked statistical significance. Harms of screening, including false-positives, anxiety, and over-treatment, were poorly studied. Furthermore, cohort studies suggested that a large proportion of persons with subclinical hypothyroidism were biochemically euthyroid after 3 years of watchful waiting, highlighting the risk of over-diagnosis and over-treatment.
In-Depth [systematic review]: A literature review was conducted (MEDLINE, Conchrane Central Register of Controlled Trials, and the Cochrane Database of Systemic Reviews) for studies of subclinical hypothyroidism and hyperthyroidism between 2002-2014, and of overt hypothyroidism and hyperthyroidism without date limitation. Researchers identified 11 trials and 1 retrospective cohort study on the treatment of subclinical hypothyroidism, as well as 2 studies on subclinical hyperthyroidism. No study addressed treatment versus no treatment of screen-detected, undiagnosed overt hypothyroidism. 3 trials were good-quality, 6 trials fair-quality, and 4 trials poor-quality. No trials were conducted in the U.S. Methodology and clinical diversity among studies prevented meta-analysis evaluation. No study compared clinical benefits or harms in persons screened versus not screened for thyroid dysfunction (a pre-determined primary question of this review).
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