Recommendation on screening adults for asymptomatic thyroid dysfunction in primary care

Abstract

his guideline from the Canadian Task Force on Preventive Health Care focuses on screening for thyroid dysfunction among asymptomatic nonpregnant adults in primary care beyond usual care and vigilance for signs and symptoms of thyroid dysfunction. Thyroid dysfunction is diagnosed based on abnormal levels of serum thyroid-stimulating hormone (TSH) and can be characterized as either hypo-or hyperthyroidism. Hypothyroidism results from impaired thyroid hormone production (i.e., thyroxine [T 4 ] or triiodothyronine [T 3 ]), leading to elevated levels of TSH. Hypothyroidism is often caused by autoimmune disorders (e.g., Hashimoto thyroiditis) or occurs as a sequela of hyperthyroidism treatment, which can render the thyroid gland nonfunctional. 1 Hyperthyroidism results from an overproduction of thyroid hormone, leading to the suppression of TSH. 1 Causes of hyperthyroidism include Graves disease, toxic multinodular goitre and toxic adenoma. 2 Signs and symptoms of thyroid dysfunction are variable between patients and often nonspecific. For hypothyroidism, symptoms may include tiredness, sensitivity to cold, dry skin, hair loss, weight gain and slowed movements and thoughts. 1,3-6 For hyperthyroidism, symptoms may include sinus tachycardia, atrial fibrillation, hyperactivity or irritability, intolerance to heat, tremor and weight loss. 1,2,7 Some people with thyroid dysfunction are asymptomatic. 8 If left untreated, hypothyroidism may increase the risk of cardiac dysfunction, hypertension, dyslipidemia, cognitive impairment and, in rare cases, myxedema coma. 3,9 Untreated hyperthyroidism may increase the risk of cardiac conditions (e.g., atrial fibrillation, heart failure) or bone fractures, and could lead to thyroid storm, an uncommon, life-threatening condition associated with tachycardia, extreme fatigue, fever and nausea. 2,10 Minor variations in thyroid function as measured by abnormal levels of TSH are often self-limiting. Observational studies have reported that levels of TSH appear to revert to normal without treatment in 37%-62% of patients with initially elevated levels and 51% with initially low levels, particularly for milder cases of thyroid dysfunction (mean follow-up 32-60 mo). 11,12 Screening is intended to detect thyroid dysfunction in asymptomatic patients in order to prevent adverse consequences of untreated thyroid dysfunction. 13 Screening is done by performing a blood test for TSH. Abnormal levels of TSH are followed up with additional diagnostic testing that often includes blood tests to measure thyroid hormone levels or other tests (e.g., ultrasound) as warranted. An estimated 10% of Canadians aged 45 years or older report that they have been diagnosed with thyroid dysfunction, and prevalence is higher in women (16%) than in men (4%). 14 Prevalence has also been reported to be higher in adults older than 85 years (16%), 14 GUIDELINE HEALTH SERVICES CPD

Age- and Sex-Specific TSH Upper-Limit Reference Intervals in the General French Population: There Is a Need to Adjust Our Actual Practices

“…Some authors advocate not initiating treatment with thyroid hormone unless TSH is above very high values [23]. This is an on-going but controversial debate [24], but regardless of the need to treat or not, current recommendations are against screening for asymptomatic thyroid dysfunction in primary care [25].…”

Comprehensive Geriatric Assessment

“…While the USPSTF does not recommend screening for thyroid function, and the Canadian Task Force on Preventive Health Care strongly recommends against screening for thyroid dysfunction in asymptomatic nonpregnant adults, the statement also comments that clinicians remain alert to signs and symptoms suggestive of thyroid dysfunction and investigate accordingly. In practice, it is common for older adults to manifest signs (appearance) and symptoms suggestive of hypothyroidism (Birtwhistle et al 2019). The American Thyroid Association Guidelines for hypothyroidism recommended in the past to begin screening at age 35 and every 5 years thereafter, particularly in women, and that it is cost-effective; the guidelines are due for revision (Ladenson et al 2000).…”

What happens when laboratory reference ranges change?

“…Screening or case-finding of asymptomatic thyroid dysfunction is not recommended in primary care. 6 Treatment of subclinical thyroid dysfunction may have no clinical benefit in the short term. 7 Indeed, treatment may have adverse effects and be associated with cardiac and skeletal risks.…”