When should Thyroid-Stimulating Hormone (TSH) levels be checked?

When to Check TSH Levels

TSH levels should be checked in high-risk individuals, symptomatic patients, and during specific clinical scenarios, but routine screening in asymptomatic adults is not universally recommended due to insufficient evidence of benefit.

High-Risk Populations Requiring TSH Testing

TSH testing is particularly indicated in the following populations:

• Elderly individuals 1, 2
• Postpartum women due to risk of postpartum thyroid dysfunction 1, 2
• Patients with Down syndrome 1, 2
• Individuals with high radiation exposure (>20 mGy) 1, 2
• Women of childbearing age before pregnancy or during first trimester 1
• Women older than 50 years with symptoms potentially caused by thyroid disease 1
• Perimenopausal and postmenopausal women with nonspecific symptoms 1

Symptomatic Patients

TSH testing is indicated in patients presenting with:

• Symptoms suggesting hypothyroidism (fatigue, weight gain, dry skin, cold intolerance, constipation) 3
• Symptoms suggesting hyperthyroidism (weight loss, heat intolerance, palpitations, anxiety)
• Unexplained mood disorders or depression (TSH abnormalities are associated with increased odds of clinically relevant depression) 4
• Atrial fibrillation of unknown etiology 1
• Unexplained cognitive decline or dementia 1

Monitoring Scenarios

TSH should be checked in the following monitoring scenarios:

• Patients on levothyroxine therapy: Every 6-8 weeks during dose adjustments and every 6-12 months once stable 2, 5
• Pregnant patients with pre-existing hypothyroidism: At minimum, during each trimester of pregnancy 5
• Pediatric patients on thyroid replacement: 2 and 4 weeks after treatment initiation, 2 weeks after any dosage change, then every 3-12 months until growth completion 5
• Patients with thyroid cancer: Regular monitoring based on target TSH suppression levels 2, 5

Special Clinical Scenarios

• Hospitalized elderly patients: Consider TSH testing as alterations in thyroid function tests are common (74.3%) and associated with poor prognosis 6
• Patients with chronic renal failure: May have altered TSH levels requiring monitoring 7
• Before initiating medications known to affect thyroid function

Controversial Areas: Routine Screening

There are conflicting recommendations regarding routine screening:

• The American Thyroid Association recommends screening all adults beginning at age 35 and every 5 years thereafter 8
• The USPSTF concludes there is insufficient evidence to recommend for or against routine screening in asymptomatic adults 1, 2
• The American Academy of Family Physicians recommends against routine screening in asymptomatic patients younger than 60 years 1

Important Considerations for TSH Testing

• High sensitivity and specificity: TSH has 98% sensitivity and 92% specificity for detecting thyroid disease 1
• Serial measurements: A single abnormal TSH value is insufficient for diagnosis; confirmation with repeat testing is recommended 2
• Timing of repeat testing: Thyroid function tests should be repeated over 3-6 month intervals in asymptomatic persons with abnormal results before making a diagnosis 1
• Exception: Immediate action may be warranted for TSH values >10.0 or <0.1 mIU/L 1

Pitfalls to Avoid

• Relying on a single TSH measurement for diagnosis 2
• Failing to recognize non-thyroidal illness (euthyroid sick syndrome) in hospitalized patients 6
• Overlooking thyroid dysfunction in patients with depression or mood disorders 4
• Not considering thyroid testing in elderly patients with nonspecific symptoms 1
• Ignoring the need for more frequent monitoring in high-risk groups 2

By following these evidence-based recommendations for TSH testing, clinicians can appropriately identify and manage thyroid dysfunction while avoiding unnecessary testing in low-risk populations.