Do you order a Thyroid-Stimulating Hormone (TSH) test and prescribe thyroid medication for suspected thyroid dysfunction?

TSH Testing and Thyroid Medication: Clinical Approach

Direct Answer

Do not routinely screen asymptomatic adults with TSH testing, but order TSH when clinical symptoms suggest thyroid dysfunction, and prescribe thyroid medication only after confirming persistent abnormalities with repeat testing over 3-6 months. 1

When to Order TSH Testing

Screen These High-Risk Populations

• Patients on immune checkpoint inhibitors (monitor monthly for 6 months, then every 3 months for 6 months, then every 6 months for 1 year) 1
• Individuals with Down syndrome (though evidence for clinical benefit remains insufficient) 2
• Patients with specific symptoms: unexplained fatigue, weight changes, hair loss, cold/heat intolerance, constipation, depression, palpitations, or tremor 1

Do NOT Routinely Screen

• The U.S. Preventive Services Task Force found insufficient evidence to recommend routine screening in asymptomatic adults, despite TSH testing being extremely common practice 1
• While TSH has 98% sensitivity and 92% specificity in specialty clinics, the positive predictive value is low in primary care screening populations 1

Critical Testing Principles

Never Diagnose on Single TSH Result

• TSH levels vary by up to 50% day-to-day, with 40% variation even at the same time of day 1
• Confirm all abnormal results with repeat testing over 3-6 months before initiating treatment 1
• TSH is affected by acute illness, medications (iodine, dopamine, glucocorticoids, amiodarone), pregnancy, adrenal insufficiency, and pituitary disorders 1

Interpret TSH Values Appropriately

• TSH >6.5 mU/L is considered elevated 1
• TSH <0.1 mU/L is considered suppressed 1
• In patients ≥80 years old, 12% have TSH >4.5 mU/L without thyroid disease—standard reference ranges are inappropriate for elderly patients 1

Follow-Up Testing Strategy

• If TSH is persistently abnormal, measure free T4 to differentiate subclinical (normal T4) from overt (abnormal T4) thyroid dysfunction 1
• For suspected hyperthyroidism with normal free T4, obtain T3 level 3
• In suspected hypophysitis (checkpoint inhibitor patients), look for low TSH with low free T4, suggesting central hypothyroidism 1

When to Prescribe Thyroid Medication

Confirmed Hypothyroidism Requiring Treatment

• Overt hypothyroidism: Elevated TSH with low free T4 4
• Start levothyroxine 1.6 mcg/kg/day in healthy adults 4
• In patients with cardiac disease or atrial fibrillation risk, start lower doses and titrate slowly every 6-8 weeks 4
• In elderly patients, use lower starting doses (<1.6 mcg/kg/day) 4

Subclinical Hypothyroidism: Exercise Caution

• Evidence shows no benefit of treating subclinical hypothyroidism on blood pressure, weight, or cardiovascular outcomes 1
• The USPSTF found poor evidence that treatment improves clinically important outcomes in screen-detected disease 1
• Despite lack of evidence, many asymptomatic patients receive treatment—the median TSH at treatment initiation has decreased from 8.7 to 7.9 mU/L over time 1

Special Populations

Pregnant Patients:

• Increase pre-pregnancy levothyroxine dose by 12.5-25 mcg/day if TSH above trimester-specific range 4
• Monitor TSH every 4 weeks until stable 4
• Return to pre-pregnancy dose immediately postpartum 4

Pediatric Patients:

• In children, subclinical hypothyroidism associates with poor cognitive development, providing stronger rationale for treatment 2
• Dosing varies dramatically by age: 10-15 mcg/kg/day for 0-3 months, decreasing to 1.6 mcg/kg/day after puberty completion 4

Checkpoint Inhibitor-Induced Hypophysitis:

• When both adrenal insufficiency and hypothyroidism are present, always start steroids before thyroid hormone to avoid precipitating adrenal crisis 1
• Both conditions typically require lifelong replacement 1

Monitoring Treatment

Primary Hypothyroidism

• Monitor TSH as the primary parameter 4, 3
• Peak therapeutic effect takes 4-6 weeks 4
• Titrate by 12.5-25 mcg increments every 4-6 weeks until euthyroid 4

Central (Secondary/Tertiary) Hypothyroidism

• TSH is unreliable for monitoring—use free T4 instead 4, 3
• Titrate to restore free T4 to upper half of normal range 4

Critical Pitfalls to Avoid

• Do not treat based on symptoms alone in Down syndrome patients—overlap between Down syndrome features and hypothyroid symptoms makes clinical diagnosis unreliable 2
• Do not ignore overtreatment risk—good evidence shows substantial overtreatment with levothyroxine occurs, though long-term harms are unknown 1
• Do not administer levothyroxine with food or other medications—give on empty stomach, 30-60 minutes before breakfast, at least 4 hours apart from interfering drugs 4
• Do not assume inadequate response means higher doses are needed—dosages >300 mcg/day suggest poor compliance, malabsorption, or drug interactions 4