How often should TSH (Thyroid-Stimulating Hormone) levels be checked in asymptomatic adults without a history of thyroid disease who present for a routine health visit?

TSH Screening in Asymptomatic Adults Without Thyroid Disease

For routine health visits in asymptomatic adults without thyroid disease, do not perform routine TSH screening under age 35, then screen every 5 years starting at age 35, with more frequent screening reserved for high-risk populations or symptomatic patients. 1, 2, 3

Evidence-Based Screening Intervals

Standard Population (Age <35)

• The American Academy of Family Physicians recommends against routine thyroid screening in asymptomatic patients younger than age 60 years 2
• The USPSTF concludes evidence is insufficient to recommend for or against routine screening, finding no controlled studies demonstrating that screening improves clinical outcomes 1, 2

Standard Population (Age ≥35)

• The American Thyroid Association recommends measuring TSH beginning at age 35 years and every 5 years thereafter 1, 2, 3
• This recommendation is particularly compelling in women but can be justified in men as a cost-effective measure during periodic health examinations 3

Women Over Age 50 with Nonspecific Symptoms

• The American College of Physicians recommends screening women older than age 50 years with one or more general symptoms that could be caused by thyroid disease 1, 2
• The Canadian Task Force recommends maintaining high clinical suspicion for nonspecific symptoms in perimenopausal and postmenopausal women 1

High-Risk Populations Requiring More Frequent Screening

Screen these patients more frequently (annually or every 1-2 years) regardless of age: 2

• Postpartum women during the first year after delivery 2
• Patients with Down syndrome, though symptom evaluation is complicated by overlapping features 1, 2
• Radiation exposure including external-beam radiation to head/neck or high-dose I131 exposure (>20 mGy) 2
• Type 1 diabetes due to increased autoimmune thyroid disease risk 2
• Elderly patients aged 85+ who are more than twice as likely to develop hypothyroidism compared to those aged 65-69 years 2

Critical Pitfalls to Avoid

Overscreening and False Positives

• Annual thyroid testing in all patients is not evidence-based and contributes to overdiagnosis and overtreatment 2
• When TSH is initially abnormal, 98% of patients with normal initial TSH remain normal within 5 years 4
• More than 50% of patients with elevated or decreased TSH levels have normal levels on repeat measurements 4
• Severe non-thyroid illness causes false-positive TSH results 2

Confirmation Before Treatment

• Always repeat TSH with free T4 after 3-6 months before diagnosing thyroid dysfunction 2, 5
• TSH levels often revert to normal spontaneously, particularly in screening programs 2
• 30-60% of mildly abnormal TSH levels normalize on repeat testing 6

Age-Specific Considerations

Very Elderly (Age >80-85)

• Age-specific reference ranges should be considered, with the upper limit of normal TSH increasing from 3.75 mIU/L at age 40 to 5.0 mIU/L at age 90 7
• The use of age-specific reference ranges reclassifies only 0.1-1.9% of participants in most age bands, but 2.1-4.7% in those aged 85+ 7
• The oldest old subjects with TSH ≤10 mIU/L should be carefully followed with a wait-and-see strategy, generally avoiding hormonal treatment 5

When NOT to Screen

Do not screen if: 1, 2

• Patient is asymptomatic and under age 35 without risk factors
• Patient had normal TSH within the past 5 years and remains asymptomatic
• Patient is acutely ill (wait until recovery to avoid false positives)

Practical Algorithm

1. Age <35, no risk factors, asymptomatic: No screening 2, 3
2. Age 35-50, no risk factors, asymptomatic: Screen every 5 years 2, 3
3. Age >50, women with nonspecific symptoms: Screen once, then every 5 years if normal 1, 2
4. High-risk populations: Screen annually or every 1-2 years 2
5. Any abnormal result: Repeat in 3-6 months with free T4 before diagnosing 2, 5