Treatment of Subclinical Hypothyroidism
Patients with subclinical hypothyroidism and TSH levels consistently above 10 mIU/L should receive levothyroxine therapy due to higher risk of progression to overt hypothyroidism (5% per year). 1
Diagnostic Confirmation
- Confirm diagnosis with repeat TSH and free T4 measurement after 2-3 months, as 30-60% of elevated TSH levels may normalize spontaneously 1, 2
- Subclinical hypothyroidism is defined as elevated TSH with normal free T4 levels 3
- Measure anti-TPO antibodies, as their presence indicates autoimmune etiology and higher risk of progression to overt hypothyroidism (4.3% vs 2.6% per year in antibody-negative individuals) 1, 3
Treatment Algorithm Based on TSH Levels
Definite Indications for Treatment:
- TSH consistently >10 mIU/L, regardless of symptoms 1, 3, 4
- All pregnant women with subclinical hypothyroidism regardless of TSH level 1
- Women planning pregnancy 3
Consider Treatment in TSH 4.5-10 mIU/L with:
- Symptomatic patients with symptoms compatible with hypothyroidism 1, 4
- Positive TPO antibodies 1, 3
- Infertility 4
- Goiter 4
- Younger patients (<65 years) with cardiovascular risk factors 5, 6
Monitoring Without Treatment (TSH 4.5-10 mIU/L):
- For patients with TSH between 4.5-10 mIU/L without risk factors, monitoring with thyroid function tests at 6-12 month intervals is recommended 1, 3
- This is particularly appropriate for elderly patients (>70 years) where treatment may be harmful 2
Levothyroxine Dosing Guidelines
- For patients <70 years without cardiac disease: start with full replacement dose of approximately 1.6 mcg/kg/day 3
- For patients >70 years or with cardiac disease: start with a lower dose of 25-50 mcg/day and titrate gradually 3
- Take levothyroxine on an empty stomach 7
- Avoid concurrent administration with iron and calcium supplements, which reduce absorption 7
Monitoring and Dose Adjustments
- Monitor TSH every 6-8 weeks while titrating hormone replacement 3
- Once adequately treated, repeat testing every 6-12 months 3
- Target TSH of 0.5-2.0 mIU/L for most patients 4
- Consider age-dependent TSH goals: upper limit of 3.6 mIU/L for patients under 40, and 7.5 mIU/L for patients over 80 2
- Wait 6-12 weeks before dose adjustments due to long half-life of levothyroxine 7
Risks and Benefits of Treatment
Benefits:
- Prevention of progression to overt hypothyroidism 1, 3
- Potential reduction in cardiovascular risk in younger patients 6
- Improvement in lipid profiles 3
Risks:
- Overtreatment leading to subclinical hyperthyroidism (occurs in 14-21% of treated patients) 1
- Increased risk of atrial fibrillation and osteoporosis with overtreatment 3, 4
- Potential harm in elderly patients with subclinical hypothyroidism 2
Common Pitfalls to Avoid
- Treating transient hypothyroidism that would normalize spontaneously 7
- Attributing non-specific symptoms to slightly elevated TSH 7
- Excessive dose increases that could lead to iatrogenic hyperthyroidism 3
- Failing to recognize drug interactions that affect levothyroxine absorption or metabolism 7
- Undertreatment leading to persistent hypothyroid symptoms 3