When to treat subclinical hypothyroidism?

When to Treat Subclinical Hypothyroidism

Treatment of subclinical hypothyroidism should be initiated in all patients with TSH >10 mIU/L, pregnant women or women contemplating pregnancy regardless of TSH level, and in symptomatic patients with TSH >7 mIU/L, while generally avoiding treatment in those with TSH <10 mIU/L who are over 65-70 years of age. 1, 2, 3

Definition and Prevalence

• Subclinical hypothyroidism is defined as elevated TSH with normal free T4 levels
• Affects approximately 10% of adults, more common in women and increases with age
• Autoimmune (Hashimoto's) thyroiditis is the most common cause 3

Diagnostic Considerations

• Confirm diagnosis with repeat thyroid function tests after 2-3 months, as 62% of elevated TSH levels may normalize spontaneously 2
• Check for thyroid peroxidase (TPO) antibodies, as positive antibodies indicate higher risk of progression to overt hypothyroidism 1, 3

Treatment Algorithm

Definite Treatment Indications:

1. TSH >10 mIU/L (regardless of symptoms) 1, 3, 4
2. Pregnant women or women contemplating pregnancy (any TSH elevation) 1
3. Patients with infertility 1

Consider Treatment In:

1. Symptomatic patients with TSH 7-10 mIU/L 2, 3
2. Patients with positive TPO antibodies 1, 5
3. Patients with goiter 1
4. Younger patients (<65 years) with cardiovascular risk factors 5, 3

Generally Avoid Treatment In:

1. Patients with TSH <7 mIU/L without symptoms 2
2. Elderly patients (>65-70 years) with mild TSH elevation 2, 5, 3
3. Patients >85 years (even with TSH up to 10 mIU/L) 1

Age-Specific Considerations

• TSH upper limits vary by age: 3.6 mIU/L for patients under 40, increasing to 7.5 mIU/L for patients over 80 2
• Treatment in elderly may be harmful rather than beneficial 2
• Younger patients with subclinical hypothyroidism have higher cardiovascular risk that may benefit from treatment 5, 3

Treatment Approach

• Levothyroxine is the standard treatment when indicated 1
• Start with full calculated dose in young patients
• Use lower starting doses in elderly patients and those with coronary artery disease 1
• Target TSH of 0.5-2.0 mIU/L in primary hypothyroidism 1

Common Pitfalls to Avoid

1. Overtreatment: Common in clinical practice and associated with increased risk of atrial fibrillation and osteoporosis 1
2. Treating based on single TSH measurement: Always confirm with repeat testing 2
3. Treating mild elevations in asymptomatic elderly: May cause more harm than benefit 2, 3
4. Ignoring age-specific TSH reference ranges: Normal TSH increases with age 2
5. Treating symptoms not due to thyroid dysfunction: In randomized controlled trials, treatment does not improve symptoms if TSH is <10 mIU/L 2

Monitoring

• For patients not treated initially, monitor TSH annually as 2-5% progress to overt hypothyroidism each year 1
• For treated patients, check TSH 6-8 weeks after starting therapy or dose adjustments 6
• Adjust monitoring frequency based on TSH levels (every 3 months for TSH 0.1-0.45 mIU/L; every 4-6 weeks for TSH <0.1 mIU/L) 6