No Clear Benefits for Thyroid Screening

The U.S. Preventive Services Task Force (USPSTF) still won't endorse screening asymptomatic patients for thyroid disorders, according to a new draft recommendation.

The agency says there is insufficient evidence to make a recommendation for or against thyroid screening in asymptomatic patients who aren't pregnant.

"People can have mild abnormalities in their thyroid tests and not have symptoms," Kirsten Bibbins-Domingo, MD, PhD, co-chair of the Task Force's recommendations, said in a statement. "We don't know enough about the health consequences of finding these individuals and treating them. We need more research in this area."

The draft recommendations were simultaneouslyreported in the Annals of Internal Medicine.

Screening and treating asymptomatic adults for thyroid dysfunction is common practice, the researchers said, but it's unclear whether that ultimately benefits them in the long run.

It seems to be particularly problematic with regard to subclinical hypothyroidism, which may be treated with levothyroxine. The USPSTF recommendations note that prescriptions for this generic drug rose 42% between 2006 and 2010, and in 2013 there were more than 23 million new prescriptions and refills "for a single name brand of thyroid hormone in the United States," they wrote.

One study published last year in JAMA Internal Medicine concluded that "given the high number of prescriptions for levothyroxine dispensed in the United States and the low prevalence of overt thyroid disease compared with other forms of thyroid dysfunction, it is reasonable to conclude that many asymptomatic persons receive treatment."

That study called for randomized, controlled trials of screening for thyroid dysfunction to provide "direct evidence of any potential benefits of this widespread practice."

Risks Versus Benefits

One argument in favor of treating subclinical thyroid dysfunction is being able to minimize potential associated risks, such as heart disease. But the Task Force concluded that the evidence of such benefits is mixed, and many of the supporting studies have significant methodological limitations.

One trial for subclinical hypothyroidism showed that treatment did seem to reduce heart disease and death, but it was limited because it didn't adjust for use of other medications that could reduce cardiovascular risks, the researchers wrote.

No quality studies have evaluated the benefits of treating subclinical hyperthyroidism, they added.

On the other hand, there's no adequate evidence of harm with thyroid dysfunction screening, but indirect evidence "points to the likelihood of important and frequent harms associated with screening," they wrote, including false-positive results, the psychological effects of labeling, and overdiagnosis and overtreatment of a condition that may revert to normal or never result in health problems.

"If screening for thyroid dysfunction is offered, clinicians should first ensure that patients clearly understand the uncertainties surrounding any potential clinical benefit of screening," they wrote, "as well as the possibility of harm this choice may engender."

Endocrine Groups Recommend Screening

USPSTF acknowledged that most of the nation's top professional societies dealing with endocrine and/or thyroid disorders do recommend screening for thyroid dysfunction.

The American Thyroid Association recommends screening in all adults who aren't pregnant starting at age 35 and continuing every 5 years thereafter.

The American Association of Clinical Endocrinologists recommends routine TSH measurement in older patients, with an emphasis on women.

"We stand by our recommendation of liberal screening in older Americans, particularly females with nonspecific symptoms," R. Mack Harrell, MD, president of AACE, told MedPage Today.

Harrell said the USPSTF draft recommendations are "conservative and population-oriented, frequently citing the lack of controlled, prospective trials showing benefit of treatment in mild hypo- and hyperthyroidism. AACE's recommendations are slanted toward the occasional significant benefits observed when mildly symptomatic individuals with mild hypo- or hyperthyroidism are treated."

"We favor the individualized assessment of all patients, an approach that would be expected from a physician organization whose primary trust is that between the individual patient and his or her doctor," Harrell added. The USPSTF 2014 commentary focuses more on the treatment of populations and the potential costs associated with liberalization of their previous conservative statements."

In 2006, three British professional associations -- the Association for Clinical Biochemistry, the British Thyroid Association, and the British Thyroid Foundation -- jointly recommended against routine screening for thyroid dysfunction in healthy adults.

Endocrinologists' Reactions

Stephanie Lee, MD, PhD, of Boston Medical Center, said the recommendation "is not a surprise" because of the high level of evidence required of USPSTF recommendations.

"This requires a large number -- thousands -- of subjects with a 'significant' outcome, like MI or death -- not just feeling tired," Lee said. "This is a problem with all endocrine research, that even well-done trials are too small to be considered 'important' evidence."

"The reason this does not make a difference to the practicing endocrinologist is because the symptoms of hypothyroidism are so broad, there is almost never a patient at risk -- usually middle-age females -- who will not qualify because of a 'symptom' such as fatigue, weight gain, dry skin, etc.," she said. "Since patients are referred to a specialist either because of abnormal thyroid function test (TFT) or because of symptoms and normal TFT, we would always be justified in thyroid testing."

The USPSTF noted that the recommendation isn't significantly changed from its 2004 recommendation. The agency will be taking public comment on the draft guidance through Nov. 24.