When to treat subclinical hypothyroidism?

When to Treat Subclinical Hypothyroidism

Treatment of subclinical hypothyroidism is recommended for patients with TSH >10 mIU/L, pregnant women or those planning pregnancy, and should be considered in symptomatic patients, those with infertility, goiter, or positive anti-TPO antibodies when TSH is between 4.5-10 mIU/L. 1, 2

Definition and Prevalence

• Subclinical hypothyroidism is defined as elevated TSH with normal free T4 and T3 levels
• Prevalence is 4-10% in the general population, reaching up to 20% in women over 60 years 3

Diagnostic Approach

• Confirm diagnosis with repeat thyroid function tests after at least 2 months, as 62% of elevated TSH levels may normalize spontaneously 4
• Rule out other causes of transient TSH elevation (recovery from illness, medication effects)

Treatment Algorithm

Definite Treatment Indications (Strong Evidence):

1. TSH >10 mIU/L - All patients should receive treatment 1, 2
2. Pregnancy or planning pregnancy - Treat regardless of TSH level to decrease risk of pregnancy complications and impaired cognitive development of offspring 2

Consider Treatment (Moderate Evidence):

1. TSH 4.5-10 mIU/L with any of the following:
   • Symptomatic patients
   • Patients with infertility
   • Presence of goiter
   • Positive anti-TPO antibodies 2
   • Age <65 years with cardiovascular risk factors 5

Monitoring Without Treatment (Initial Approach):

1. TSH <7 mIU/L in asymptomatic patients 4
   • Monitor every 6-12 months 1
   • Observe for progression to overt hypothyroidism (occurs at rate of 2-5% annually) 2

Age-Specific Considerations

• Younger patients (<65 years): Lower threshold for treatment due to increased cardiovascular risk 5
• Elderly patients (>85 years): Treatment should likely be avoided if TSH ≤10 mIU/L 2, 3
• Age-dependent TSH goals: Upper limit of normal is 3.6 mIU/L for patients <40 years and 7.5 mIU/L for patients >80 years 4

Cardiovascular Risk Considerations

• Subclinical hypothyroidism is associated with:
  • Atherogenic lipid profile
  • Hypercoagulable state
  • Diastolic dysfunction
  • Impaired vascular function
  • Increased risk of coronary heart disease (especially with TSH ≥10 mIU/L) 6, 3
• Treatment may improve lipid profiles and cardiac abnormalities, particularly in patients with higher initial TSH levels 3

Treatment Approach

• Levothyroxine is the standard treatment
• Target TSH: 0.5-2.0 mIU/L in primary hypothyroidism 2
• Monitor TSH 6-8 weeks after starting therapy or dose adjustments 1
• Once stable, monitor every 6-12 months 1

Common Pitfalls

1. Overtreatment: Can occur in 14-21% of treated patients, resulting in subclinical hyperthyroidism with increased risk of cardiac arrhythmias and bone loss 1
2. Treating based on single TSH measurement: Always confirm with repeat testing after 2 months 4
3. Treating asymptomatic patients with mildly elevated TSH: Treatment does not improve symptoms or cognitive function if TSH <10 mIU/L in randomized controlled trials 4
4. Ignoring age-specific considerations: Treatment may be harmful in elderly patients with subclinical hypothyroidism 4, 3