Treatment of Subclinical Hypothyroidism
Treatment should be initiated when TSH is persistently greater than 10 mIU/L, regardless of symptoms, while TSH levels between 4.5-10 mIU/L require treatment only in specific high-risk populations including pregnant women, those with positive thyroid antibodies, goiter, cardiovascular risk factors in younger patients (<65-70 years), or symptomatic patients. 1, 2, 3
TSH-Based Treatment Algorithm
TSH >10 mIU/L
- Initiate levothyroxine therapy in all patients with persistently elevated TSH above 10 mIU/L 1, 3, 4, 5
- Confirm the diagnosis with repeat testing at least 2 months later, as 62% of elevated TSH levels may spontaneously normalize 5
TSH 4.5-10 mIU/L
Treatment is indicated in the following specific populations:
- Pregnant women or those contemplating pregnancy to prevent pregnancy complications and impaired fetal neurocognitive development 6, 3
- Patients with positive anti-TPO antibodies, which increase annual progression risk to overt hypothyroidism (4.3% vs 2.6% without antibodies) 1, 2, 6
- Patients with goiter 1, 6
- Symptomatic patients with hypothyroid symptoms 6, 4
- Younger patients (<65-70 years) with cardiovascular risk factors, as observational data suggests levothyroxine may reduce coronary heart disease risk in this population 2, 7, 4
- Children with underlying conditions such as Hashimoto's thyroiditis with progressive deterioration, Turner syndrome, or Down syndrome 1
- Patients with proatherogenic metabolic abnormalities such as elevated LDL cholesterol 1
When NOT to Treat
- Avoid treatment in patients >85 years old with TSH ≤10 mIU/L, as treatment may be harmful in elderly patients 6, 5
- Do not treat asymptomatic patients with TSH <7-10 mIU/L without other risk factors, as double-blinded randomized controlled trials show no improvement in symptoms or cognitive function 5
- Wait-and-see strategy is appropriate for mild subclinical hypothyroidism, as thyroid function normalizes spontaneously in up to 40% of cases 7, 4
Levothyroxine Dosing Strategy
Standard Dosing
- Full replacement dose is 1.6 mcg/kg/day for most young patients without cardiac disease 1, 6
- Target TSH of 0.5-2.0 mIU/L in primary hypothyroidism 6
Special Populations Requiring Lower Starting Doses (25-50 mcg/day)
- Patients >60 years old 8, 6, 3
- Patients with known or suspected coronary artery disease to avoid precipitating cardiac complications 2, 6, 3
- Patients with long-standing severe hypothyroidism 6
- Children with cardiac disease or multiple comorbidities 1
Pregnancy Considerations
- Increase weekly levothyroxine dosage by 30% immediately upon pregnancy confirmation (take one extra dose twice per week) 8, 3
- Monitor TSH monthly during pregnancy and adjust dosing accordingly 8
- Return to pre-pregnancy dose immediately after delivery 8
Critical Pitfalls to Avoid
Overtreatment Risks
- Iatrogenic subclinical hyperthyroidism occurs in 14-21% of treated patients and increases risk of atrial fibrillation (especially in elderly), bone loss, and cardiac complications 1, 2, 6
- Atrial fibrillation is the most common arrhythmia observed with levothyroxine overtreatment in elderly patients 8
Age-Dependent TSH Goals
- TSH upper limit of normal is age-dependent: 3.6 mIU/L for patients <40 years, increasing to 7.5 mIU/L for patients >80 years 5
- Avoid aggressive TSH suppression in elderly patients, as higher TSH levels are physiologically normal with aging 5
Monitoring Considerations
- Closely monitor infants during the first 2 weeks of levothyroxine therapy for cardiac overload and arrhythmias 8
- If TSH remains elevated despite adequate replacement dose, evaluate for poor compliance, malabsorption, or drug interactions 6