USPSTF: Evidence to Support Thyroid Screening is Inconclusive

The US Preventive Task Force (USPSTF) has found insufficient evidence for any recommendation for or against thyroid screening in asymptomatic adults [Ann Intern Med. 2014; DOI:10.7326/M14-1456]. The results echo those of the USPSTF report from a decade ago.

Additional research is still needed to determine the risks and benefits of thyroid screening and treatment, the study’s authors noted.

J. Bruin Rugge, MD, MPH, Oregon Health & Science University, Portland, Oregon, and colleagues 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 report from April 2011. The proportion of community-dwelling people ≥65 years of age receiving thyroid hormone had more than doubled, increasing from 8.1% in 1989 to 20% in 2005.

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 researchers found no trials comparing benefits or harms in screened versus not screened people and no trials assessing treatment versus no treatment of screen-detected undiagnosed overt hypothyroidism. They found 11 trials and 1 retrospective study on subclinical hypothyroidism treatment and 2 studies evaluating subclinical hyperthyroidism treatment.

The authors rated only 3 of the subclinical hypothyroidism treatment trials as good quality, and none of the trials was conducted in the United States. In 1 fair-quality trial comparing treatment with levothyroxine versus 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 individuals >70 years of age.

In 5 of the trials, the researchers found no difference between treatment and placebo for measure of quality of life. In 1 good-quality trial, they found no association between treatment with levothyroxine versus placebo on cognitive function, and in 3 trials they found no effects on blood pressure between treatment and no treatment.

The results on metabolic risks were also inconclusive. Three trials found statistically significant differences in mean total cholesterol levels, 3 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 study’s authors noted.

The researchers concluded, "[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.”—Kerri Fitzgerald