Evidence on Thyroid Screening Effects Remains Inconclusive

Larry Hand

October 28, 2014

Ten years after finding insufficient evidence to recommend for or against thyroid screening in asymptomatic adults, the US Preventive Services Task Force (USPSTF) again has found insufficient evidence for any recommendation, according to an article published online October 27 in the Annals of Internal Medicine.

More research is still needed to determine the risks and benefits of thyroid screening and treatment, the authors of the report write.

J. Bruin Rugge, MD, MPH, and colleagues from the Oregon Health & Science University in Portland, conducted a systematic analysis of English-language randomized controlled trials and observational studies of screening and treatment for subclinical and undiagnosed overt hypothyroidism and hyperthyroidism in adults without goiter or thyroid nodules.

The prescribing rate for the thyroid medication levothyroxine increased from 49.8 million in 2006 to 70.5 million in 2010, according to the IMS Institute for Healthcare Informatics April 2011 report. The proportion of community-dwelling people older than 65 years receiving thyroid hormone more than doubled, going from 8.1% in 1989 to 20% in 2005, according to another report.

The researchers sought to determine whether screening for thyroid dysfunction reduced morbidity and mortality, whether it created risk for harms, whether screen-detected thyroid dysfunction improved outcomes, and whether any harms resulted from treating screen-detected thyroid dysfunction.

The found no trials comparing benefits or harms in screened vs not screened people and no trials assessing treatment vs no treatment of screen-detected undiagnosed overt hypothyroidism. They found 11 trials and one retrospective study on subclinical hypothyroidism treatment and two studies evaluating subclinical hyperthyroidism treatment.

No US Trials

The authors rated only three of the subclinical hypothyroidism treatment trials as good quality, and none of the trials was conducted in the United States. In one fair-quality trial comparing treatment with levothyroxine vs no treatment, levothyroxine was associated with lower risk for ischemic heart disease, all-cause mortality death resulting from circulatory diseases, and cancer death, but the association did not remain for people older than 70 years.

In five of the trials, the researchers found no difference between treatment and placebo for measure of quality of life. In one good-quality trial, they found no association between treatment with levothyroxine vs placebo on cognitive function, and in three trials they found no effects on blood pressure between treatment and no treatment.

Results were mixed for metabolic risks. Three trials found statistically significant differences in mean total cholesterol levels, three trials found statistically significant differences in mean low-density lipoprotein cholesterol, and no trials found significant differences between treatment and no treatment for high-density lipoprotein cholesterol or triglyceride values.

No trials found a meaningful difference between treatment and no treatment for body mass index or weight.

"As in the 2004 USPSTF review, we found no direct evidence on effects of thyroid screening versus no screening on clinical outcomes," the authors write.

They recommend that trials be conducted on the treatment of subclinical hypothyroidism vs placebo or no treatment in screen-detected populations, "because determining treatment efficiency is a prerequisite for effective screening interventions."

Emerging research, they write, suggests subclinical hypothyroidism may be protective in older individuals. "Additional research to clarify criteria for abnormal thyroid function would have important implications for defining the target populations and understanding the effect of screening."

They conclude, "[S]creening 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."

This research was supported by a grant from the Agency for Healthcare Research and Quality, US Department of Health and Human Services. The authors have disclosed no relevant financial relationships.

Ann Intern Med. Published online October 27, 2014. Full text

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