Treatment for TSH >150 mIU/L
Initiate levothyroxine immediately at 1.6 mcg/kg/day for patients under 70 years without cardiac disease, or start at 25-50 mcg/day for elderly patients or those with cardiac disease, as this represents severe overt hypothyroidism requiring urgent treatment. 1
Immediate Assessment Required
Before initiating treatment, you must:
- Rule out adrenal insufficiency first - in patients with suspected central hypothyroidism or concurrent adrenal disease, start corticosteroids several days before levothyroxine to prevent adrenal crisis 1, 2
- Measure free T4 to confirm overt hypothyroidism (will be low with TSH >150) 1
- Check anti-TPO antibodies to confirm autoimmune etiology (Hashimoto's thyroiditis) 1
- Assess for myxedema coma symptoms (altered mental status, hypothermia, bradycardia, hypotension) which requires ICU admission and IV levothyroxine 3, 4
Initial Dosing Algorithm
For patients <70 years without cardiac disease:
- Start full replacement dose of 1.6 mcg/kg/day 1, 5, 3
- This TSH level indicates severe hypothyroidism requiring aggressive treatment 1
- Monitor TSH and free T4 in 6-8 weeks 1
For patients ≥70 years OR with cardiac disease:
- Start at 25-50 mcg/day 1, 5, 3
- Increase by 12.5-25 mcg every 6-8 weeks based on TSH response 1
- Elderly patients with coronary disease risk cardiac decompensation even with therapeutic doses 5, 3
For pregnant patients:
- Start 1.6 mcg/kg/day immediately 2
- Monitor TSH every 4 weeks during pregnancy 2
- Untreated hypothyroidism causes preeclampsia, low birth weight, and neurodevelopmental effects 1
Monitoring Protocol
- Recheck TSH and free T4 every 6-8 weeks during dose titration 1, 2
- Target TSH: 0.5-4.5 mIU/L (aim for 0.5-2.0 mIU/L) 1, 5
- Once stable, monitor every 6-12 months 1
- For cardiac patients or atrial fibrillation, consider testing within 2 weeks after dose changes 1
Dose Adjustments
- Increase by 12.5-25 mcg if TSH remains elevated after 6-8 weeks 1
- Larger increments (25 mcg) appropriate for younger patients without cardiac disease 1
- Smaller increments (12.5 mcg) mandatory for elderly or cardiac patients 1
- Wait full 6-8 weeks between adjustments to reach steady state 1
Critical Pitfalls to Avoid
- Never start levothyroxine before ruling out adrenal insufficiency - this can precipitate life-threatening adrenal crisis 1, 2, 5
- Do not use excessive initial doses in elderly or cardiac patients - risk of angina, arrhythmias, or cardiac decompensation 5, 3
- Avoid adjusting doses too frequently - levothyroxine takes 6-8 weeks to reach steady state 1
- Check compliance before increasing dose - 25% of "resistant" cases are actually non-compliance 1, 6
- Screen for malabsorption if TSH remains >150 despite adequate dosing - consider celiac disease, atrophic gastritis, or medications interfering with absorption 5, 6
Special Considerations for Severe Hypothyroidism
With TSH >150, consider:
- Myxedema coma risk - requires ICU admission, IV levothyroxine 200-400 mcg loading dose, then 50-100 mcg daily IV 3, 4
- Cardiac dysfunction - severe hypothyroidism causes delayed relaxation and abnormal cardiac output 1
- Progression risk - TSH >10 carries 5% annual progression risk to worsening hypothyroidism if untreated 1
- Malabsorption testing - if TSH remains severely elevated on 500 mcg/day, perform single-dose absorption test (1000 mcg oral dose with TSH/T4 measured at 4 hours) 6