New guidance urges Canadian physicians to rethink their practices on assessing and treating routine thyroid dysfunction. Studying the benefits, harms, and costs of treating asymptomatic adults with abnormal thyroid stimulating hormone (TSH) tests, the Canadian Task Force on Preventive Health Care asserts that treatment for screen-detected hypothyroidism would do little to improve clinical outcomes. The findings have implications beyond primary care practices. “If the guidelines are followed it will mean a decrease in the TSH test volume for clinical labs,” Richard Birtwhistle, MD, MSc, CCFP, FCFP, emeritus professor of Family Medicine and Public Health Sciences at Queen’s University and chair of the task force’s thyroid dysfunction working group, told CLN Stat.
Birtwhistle and colleagues did a systematic review of studies related to thyroid dysfunction screening, using the Grading of Recommendations, Assessment, Development, and Evaluation, or GRADE, approach to rate outcomes and determine recommendation strength. In their research, they found no trials of screening for thyroid dysfunction. Instead, their analysis consisted of 19 randomized trials and three cohort studies that chronicled treatment of screen-detected patients, Birtwhistle said. Investigators looked for differences in mortality (total and cardiovascular), cardiovascular events (fatal and nonfatal myocardial infarction, atrial fibrillation), fractures, thyroid specific quality of life, cognitive function, and intermediate outcomes such as blood pressure and cholesterol.
Overall, the studies found no differences in these outcomes. Several studies that compared men and women treated or not treated with levothyroxine for hypothyroidism, for example, found no differences in all-cause mortality or cardiovascular events.
These guidelines hopefully will prevent unnecessary treatment of healthy individuals, Omar El Kawkgi, MD, and Juan Brito, MBBS, wrote in a related editorial. “Liberal screening by testing thyroid stimulating hormone levels is a common practice that likely uncovers subclinical disease for which treatment has not been shown to improve outcomes and which may lead to overdiagnosis- and overtreatment-related harms,” they summarized.
Thyroid disease incidence in asymptomatic people with an abnormal TSH test result is actually quite low. In addition, a number of factors such as assay interference, drugs, and autoimmune disease can affect TSH values, leading to false-positive results and misclassifying individuals with disease. Finding thyroid dysfunction in asymptomatic adults also runs the risk of harm, the editorialists continued.
“Studies of treatment with levothyroxine (to normalize TSH levels) have not shown significant benefit in this population,” wrote El Kawkgi and Brito.
The guideline does not apply to adults with thyroid disease risk factors such as previously diagnosed disease or thyroid surgery, symptoms suggesting an over- or underactive thyroid gland, exposure to previous head or neck radiation or medications known to affect thyroid function, or pituitary or hypothalamic diseases. It’s also not applicable to those with symptoms indicative of thyroid dysfunction, such as irregular heart rhythms, hair loss, sensitivity to heat or cold, fatigue, or weight changes.
Clinicians should remain alert to any signs or symptoms of thyroid dysfunction in patients, Birtwhistle and colleagues recommended.
The task force guideline, which aligns with guidance from the British Columbia Ministry of Health and Toward Optimized Practice from Alberta, has won support from other Canadian medical groups.
Expert bodies in the United States have taken other paths. In 2015, the U.S. Preventive Services Task Force concluded that there was insufficient evidence to recommend for or against screening in asymptomatic, nonpregnant adults. In other U.S. guidelines, the American Thyroid Association and American Association of Clinical Endocrinologists recommend screening in older people and identifying people with overt hypothyroidism. This particular recommendation, however, was issued in 2012 and fails to reflect the latest clinical evidence on levothyroxine, which showed little benefit in patients with subclinical hypothyroidism, noted El Kawkgi and Brito.
The Canadian guidelines were based on low-quality evidence, due to the fact that the researchers couldn’t identify any direct studies on thyroid screening trials. The editorialists suggested that future trials on this topic should focus on never-before studied populations such as young people with subclinical hypothyroidism who either have signs or no signs of disease.