Don't Screen for Thyroid Problems in Asymptomatic Patients

The Canadian Task Force on Preventive Health Care has issued a strong recommendation against routine thyroid screening in nonpregnant adults without symptoms in the primary care setting, saying there is insufficient evidence of clinical benefit from the treatment of thyroid dysfunction in such individuals.

The guideline was published online November 17 in the Canadian Medical Association Journal (CMAJ) and was funded by the Public Health Agency of Canada.

"If you are a clinician who orders thyroid-stimulating hormone (TSH) tests as part of preventive health visits, we would like you to reconsider this practice. The evidence isn't there to suggest a health benefit for this type of screening as a routine part of care," says Richard Birtwhistle, MD, chair of the Task Force Thyroid Dysfunction working group, in a press statement from CMAJ.

"Given the lack of clinical effectiveness and the burden on patients, including financial costs, screening patients without symptoms consumes resources that could be better used elsewhere," added Birtwhistle, professor emeritus of family medicine and public health sciences at Queen's University, in Kingston, Ontario, Canada.

This advice differs from the recommendations of other groups, as consensus on the issue is lacking, note the authors of an accompanying editorial.

"The recommendation represents a change in thinking about screening for thyroid dysfunction and contradicts other medical society recommendations that favor screening, particularly among older people," write Juan Brito, MD, and Omar El Kawkgi, MD, of the Department of Endocrinology, Mayo Clinic, in Rochester, Minnesota.

Specifically, the position of the American Thyroid Association (ATA), published as joint guidelines with the American Association of Clinical Endocrinologists (AACE), is that screening for hypothyroidism in patients older than age 60 should be considered.

But Brito and El Kawkgi note that the ATA/AACE guidelines were released in 2012 and therefore "could not consider clinical evidence published over the last 7 years, which has shown lack of benefit of levothyroxine treatment in people with subclinical hypothyroidism."

However, the US Preventive Services Task Force issued an updated guideline in 2015 recommending against screening for thyroid dysfunction based on insufficient evidence, they point out, and that position has also been endorsed by the American Academy of Family Physicians, editorialist El Kawkgi told Medscape Medical News.

Systematic Review Included 22 Studies

Routine testing for thyroid dysfunction is commonly ordered by checking the "TSH box" on a blood test requisition form, although practice varies by primary care practitioner. An abnormal TSH level may indicate an underactive (hypothyroidism) or overactive thyroid gland (hyperthyroidism).

For its review of the evidence, the Canadian Task Force evaluated findings from 22 eligible studies, including 19 randomized clinical trials (RCTs) and three cohort studies.

Although no trials were identified that directly compared screening to no screening for thyroid dysfunction, the studies provide indirect evidence of a lack of clinical benefit of the treatment of asymptomatic thyroid dysfunction, with follow-up ranging from 3 to 36 months in the RCTs and a median follow-up of 5.0 to 7.6 years in the cohort studies, the task force says.

Evidence against screening includes the observation that factors such as some medications, autoimmune diseases, or assay variations, may explain abnormal TSH levels, and studies show those abnormalities will commonly normalize on their own in subsequent testing.

The new recommendation "is pretty straightforward," Birtwhistle emphasized in an accompanying CMAJ podcast. "We're quite confident. Canadian adults who are asymptomatic don't need to be screened for thyroid dysfunction, either hypothyroidism or hyperthyroidism."

Levothyroxine Overuse an Ongoing Concern

Furthermore, a lack of benefit has been demonstrated in the treatment of subclinical hypothyroidism with levothyroxine, despite the treatment being widely practiced, says the Canadian Task Force.

For example, as reported by Medscape Medical News, an international panel of experts concluded earlier this year that patients with subclinical hypothyroidism should not be routinely offered thyroid replacement therapy, amid evidence of no benefit to quality of life or symptoms.

"Overwhelmingly, there doesn't seem to be a treatment effect [of levothyroxine]," Birtwhistle notes in the podcast.

And levothyroxine overuse is an ongoing concern, El Kawkgi told Medscape Medical News.

"Levothyroxine is the most commonly prescribed medication in the United States, and the number of dispensed prescriptions has increased by around 40% in the last few years," he said.

"As the prevalence and incidence of overt hypothyroidism are stable, subclinical disease is likely a driver: disease which may have been identified through screening given its lack of presenting symptoms by definition," El Kawkgi noted.

Guideline Not Applicable to Symptomatic Patients

The guideline recommendation does not extend to patients who do have symptoms suggestive of hypo- or hyperthyroidism, including fatigue, cold or heat sensitivity, unexplained weight loss, hair loss, or heart rate irregularities, the task force stresses.

Such patients should visit their primary care practitioner.

In addition, the recommendation does not apply to those at higher risk for thyroid dysfunction, including those with previously diagnosed thyroid disease or thyroid surgery; exposure to medications known to affect thyroid function (eg, lithium, amiodarone); exposure to thyroid radioiodine therapy or radiotherapy to the head or neck area; or pituitary or hypothalamic diseases.

TSH Screening Common

Although data are lacking on rates of screening for thyroid dysfunction, the editorial cites one primary care study out of Toronto showing as many as 71% of patients over the age of 20 without known thyroid disease not receiving thyroid medication had received TSH testing over a 2-year period.

The new guideline may help prevent unnecessary screening, the editorialists write.

"By issuing a strong recommendation against population screening for thyroid dysfunction, the task force may help physicians to stop uncovering a large reservoir of people with mild thyroid dysfunction who are unlikely to benefit from identification or treatment, thereby preventing the overdiagnosis and overtreatment of otherwise healthy people," they note.

They add that when it comes to the goal of patient-centered care — using the best evidence to respond to the needs and desires of each individual patient — screening for thyroid dysfunction fails to measure up.

"Care that responds poorly to a person's situation, is not evidence-based, or fails to align with the patient's priorities and preferences is unlikely to be helpful and could be harmful," the editorialists write.

"One common practice that may not represent patient-centered care is screening for thyroid dysfunction," they add.

Birtwhistle concludes in the podcast that although a TSH test is not expensive, "which is a common argument for blood tests...[If] it comes back positive, that's just the start of the cascade. It may result in further testing, like a thyroid ultrasound. And it can certainly result in lifelong unnecessary treatment."

CMAJ. Published November 18, 2019. Study, Editorial, Podcast

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