When should a Thyroid-Stimulating Hormone (TSH) test be ordered?

When to Order TSH Test

TSH testing should be ordered for patients with symptoms suggestive of thyroid dysfunction, high-risk individuals, and in specific clinical scenarios where thyroid abnormalities are suspected, rather than as routine screening for all asymptomatic individuals.

Symptomatic Patients

• Order TSH when patients present with symptoms suggestive of hypothyroidism such as fatigue, weight gain, hair loss, cold intolerance, constipation, depression, and other recognized symptoms 1, 2

• Test TSH when patients present with symptoms suggestive of hyperthyroidism including weight loss, palpitations, heat intolerance, tremor, and diarrhea 1, 2

• Consider TSH testing when patients present with atrial fibrillation, especially in elderly patients, as subclinical hyperthyroidism has been associated with atrial fibrillation 1

High-Risk Populations

• Test TSH in high-risk individuals including:

  • Elderly patients 1
  • Postpartum women 1
  • Patients with history of high levels of radiation exposure (>20 mGy) 1
  • Patients with Down syndrome 1
  • Patients with type 1 diabetes 1
  • Patients on immune checkpoint inhibitor therapy 1

• Consider TSH testing in women of childbearing age before pregnancy or during the first trimester, as recommended by the American Association of Clinical Endocrinologists 1

• Test TSH in women older than 50 years with one or more general symptoms that could be caused by thyroid disease, as recommended by the American College of Physicians 1

Monitoring Scenarios

• Monitor TSH every 4-6 weeks in patients receiving immune checkpoint inhibitor therapy, as thyroid dysfunction is reported in 6-20% of these patients 1

• Check TSH in children with type 1 diabetes at diagnosis when clinically stable or soon after glycemic control has been established, then every 1-2 years or sooner if symptoms develop 1

• Monitor TSH in patients on levothyroxine therapy:

  • 6-8 weeks after any dosage change 3
  • Every 6-12 months in stable adult patients 3
  • More frequently in pediatric patients: 2 and 4 weeks after treatment initiation, 2 weeks after any dosage change, then every 3-12 months until growth is completed 3

• Test TSH in pregnant patients with pre-existing hypothyroidism as soon as pregnancy is confirmed and at minimum during each trimester 3

Testing Approach

• When testing for suspected thyroid dysfunction, TSH is the preferred initial test due to its high sensitivity (98%) and specificity (92%) 1, 4

• If TSH is abnormal, follow up with free T4 testing to further narrow the diagnosis 4

  • High TSH with low free T4 indicates primary hypothyroidism
  • Low TSH with high free T4 indicates hyperthyroidism
  • Low TSH with low free T4 suggests central hypothyroidism (evaluate for hypophysitis) 1

• Consider obtaining T3 levels if TSH is undetectable and free T4 is normal 4

Cautions and Limitations

• Be aware that TSH has a low positive predictive value when used for screening in primary care populations 1

• Interpretation of TSH results may be complicated by underlying illness or frailty of the individual 1

• TSH levels may be misleading in severe non-thyroid illness (euthyroid sick syndrome) 1, 5

• When monitoring central hypothyroidism (pituitary or hypothalamic dysfunction), TSH cannot be used reliably - use free T4 and T3 concentrations instead 4

• Consider that multiple tests over a 3-6 month interval may be needed to confirm or rule out abnormal findings 1