1. The US Preventive Services Task Force (USPSTF) found insufficient evidence to evaluate the potential benefits and harms of thyroid dysfunction screening for asymptomatic, non-pregnant adults.
2. Although laboratory testing can reliably identify abnormal TSH levels, there is no consensus on the clinical relevance of such levels in asymptomatic adults.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Although altered levels of thyroid hormones can cause a number of short- and long-term symptoms, the role for testing thyroid function in patients without symptoms is unclear. To address this, the USPSTF updated a 2004 literature review and recommendation statement on thyroid function testing in asymptomatic, non-pregnant adults. Although potential benefits of treating asymptomatic thyroid dysfunction have been suggested, ranging from improved quality of life and cognitive function to reduced risk of ischemic heart disease, evidence supporting these benefits was lacking. Furthermore, several theoretical risks of testing were found, such as potential over-diagnosis, harm from treating false-positive results, and psychological injury resulting from labeling individuals as ill. These risks were compounded by unclear reference standards for what actually constitutes an “abnormal” thyroid function test result in an asymptomatic individual, given a lack of high-quality, long-term studies comparing test results to clinical outcomes. The primary limitation of this recommendation is evident in its conclusion: high quality studies evaluating risks and benefits of thyroid dysfunction testing in asymptomatic individuals are missing from the literature. Overall, the USPSTF found limited evidence for its recommendation, but provides a clear call for further research into this under-studied screening paradigm.
In-Depth [systematic review]: This is an update of the USPSTF’s 2004 recommendation statement on thyroid function screening in asymptomatic adults. This paper reviewed evidence on screening for and treatment of four types of asymptomatic, biochemically-defined thyroid dysfunction: subclinical hypothyroidism (i.e., normal thyroxine or T4, elevated thyroid stimulating hormone or TSH), “overt” hypothyroidism (low T4, elevated TSH), subclinical hyperthyroidism (normal T4 and triiodothyronine or T3, low TSH), and “overt” hyperthyroidism (elevated T4 or T3, low TSH). Within each of these categories, evidence on harms and benefits was limited; when good- or fair-quality trails had been conducted, results were not statistically significant or deemed to be hypothesis-generating, not proof of effect. However, updating its 2004 recommendation, evidence is now sufficient to conclude that laboratory testing can reliably identify abnormal TSH levels, but there remains no clear consensus on the clinical relevance of abnormal levels in asymptomatic, non-pregnant adults.
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