When should treatment be initiated in patients with hypothyroidism (underactive thyroid gland)?

When to Start Treatment in Hypothyroidism

Treatment should be initiated immediately for all patients with overt hypothyroidism (elevated TSH with low free T4) and for those with subclinical hypothyroidism (normal free T4) when TSH is >10 mIU/L. 1, 2

Diagnostic Categories and Treatment Indications

Overt Hypothyroidism

• Definition: Elevated TSH with low free T4
• Recommendation: Immediate treatment with levothyroxine for all patients 1, 3
• Rationale: Clear clinical benefit in reducing symptoms and preventing complications

Subclinical Hypothyroidism

• Definition: Elevated TSH with normal free T4

• Treatment recommendations based on TSH levels:

  1. TSH >10 mIU/L:

     • Treat all patients under 65-70 years of age 2
     • Benefits outweigh risks for most patients

  2. TSH 4.0-10.0 mIU/L:

     • Consider treatment in:
       • Symptomatic patients 2
       • Patients with positive thyroid peroxidase (TPO) antibodies 2
       • Patients with goiter 3
       • Women planning pregnancy or currently pregnant 1, 4
       • Patients with infertility 3
     • Monitor without treatment in:
       • Asymptomatic patients without risk factors 5
       • Elderly patients >80-85 years (use "wait-and-see" approach) 2

Special Populations

Pregnant Women

• Treat all pregnant women with any degree of hypothyroidism 4, 2
• Increase levothyroxine dose by approximately 30% upon confirmation of pregnancy 1, 4
• Monitor TSH monthly during pregnancy 1
• Maintain trimester-specific TSH reference ranges 1

Elderly Patients (>65-70 years)

• Consider age-specific reference ranges for TSH 2
• Start with lower doses of levothyroxine (12.5-50 mcg daily) 1, 4, 6
• For patients >80-85 years with TSH ≤10 mIU/L, consider observation rather than treatment 2
• Monitor closely for cardiac effects of treatment 4

Patients with Cardiovascular Disease

• Start at lower doses (12.5-50 mcg daily) 1, 4, 6
• Increase dose gradually to avoid precipitating cardiac events 4

Treatment Approach

Initial Dosing

• Standard adult dosing: 1.5-1.8 mcg/kg/day 1, 6
• Elderly or cardiac patients: 12.5-50 mcg/day 1, 4, 6
• Central hypothyroidism: Dose based on free T4 levels rather than TSH 1

Monitoring and Dose Adjustment

• Check TSH and free T4 6-8 weeks after initiation or dose adjustment 1
• Target TSH: 0.5-2.5 mIU/L for most adults 2
• For central hypothyroidism: maintain free T4 in upper half of normal range 3
• Once stable, monitor annually 1

Common Pitfalls to Avoid

1. Treating based on single TSH measurement:

   • 30-60% of elevated TSH values normalize on repeat testing 5
   • Confirm abnormal TSH with repeat measurement after 2-3 months 2

2. Overlooking transient hypothyroidism:

   • Some cases resolve spontaneously and don't require lifelong treatment 5

3. Inadequate symptom assessment after treatment:

   • Approximately 25% of patients experience persistent symptoms despite normalized TSH 7
   • Reassess treatment response after 3-4 months of therapy 2
   • Consider discontinuing therapy if symptoms don't improve in subclinical cases 2

4. Medication interactions:

   • Iron and calcium supplements reduce levothyroxine absorption 5
   • Take levothyroxine on an empty stomach 5

5. Overtreatment risks:

   • Can lead to atrial fibrillation and osteoporosis, especially in elderly 3, 5
   • Monitor for signs of thyrotoxicosis (tachycardia, tremor, sweating) 5

By following these evidence-based guidelines, clinicians can appropriately identify patients who will benefit from thyroid hormone replacement while avoiding unnecessary treatment in those unlikely to benefit.