From the Guidelines
Patients with subclinical hypothyroidism and serum TSH higher than 10 mIU/L should be treated with levothyroxine therapy. This recommendation is based on the study by 1, which suggests that treatment may potentially prevent the manifestations and consequences of hypothyroidism in those patients who do progress. The rate of progression to overt hypothyroidism is 5% in patients with TSH levels higher than 10 mIU/L, compared to those with lower levels of TSH.
Diagnosis and Treatment
Subclinical hypothyroidism is a mild form of thyroid dysfunction characterized by elevated thyroid-stimulating hormone (TSH) levels with normal free thyroid hormone levels. The standard treatment is levothyroxine (T4), typically starting at 25-50 mcg daily for most adults, with lower doses (12.5-25 mcg) for elderly patients or those with heart disease. Medication should be taken on an empty stomach, 30-60 minutes before breakfast or 3-4 hours after the last meal of the day.
- TSH levels should be checked 6-8 weeks after starting treatment, with dose adjustments made in 12.5-25 mcg increments until TSH normalizes (typically 0.5-4.5 mIU/L).
- Regular monitoring is essential, with TSH checks every 6-12 months once stable.
- Treatment benefits include preventing progression to overt hypothyroidism, potentially reducing cardiovascular risk, and improving quality of life by alleviating symptoms like fatigue, cold intolerance, and mild cognitive impairment.
Special Considerations
For patients with TSH levels between 4.5 and 10 mIU/L, a trial of levothyroxine may be considered if symptoms compatible with hypothyroidism are present, as suggested by 1. However, the likelihood of improvement is small, and the decision to continue therapy should be based on clear symptomatic benefit. Physicians and patients must understand the natural history of subclinical hypothyroidism and the small but definite risk of progression to overt hypothyroidism.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Diagnosis of Subclinical Hypothyroidism
- Subclinical hypothyroidism is characterized by elevated thyroid-stimulating hormone (TSH) levels with normal thyroxine (T4) levels 2, 3, 4, 5, 6
- The diagnosis should be confirmed by repeat thyroid function tests ideally obtained at least 2 months later, as 62% of elevated TSH levels may revert to normal spontaneously 2
- TSH levels increase with age, and the upper limit of normal varies by age, with a 97.5 percentile of 3.6 mIU/L for patients under age 40 and 7.5 mIU/L for patients over age 80 2
Treatment of Subclinical Hypothyroidism
- Treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L 2, 3, 4, 5, 6
- Levothyroxine therapy is the standard treatment, but it may not improve symptoms or cognitive function if the TSH is less than 10 mIU/L 2, 3
- Treatment may be beneficial for patients under age 65 with subclinical hypothyroidism, but it may be harmful in elderly patients 2, 6
- A wait-and-see strategy is advocated for patients with mild subclinical hypothyroidism, as some cases may resolve spontaneously 3, 4
- Treatment might be indicated for patients with subclinical hypothyroidism and serum TSH levels of 10 mU/L or higher, or for young and middle-aged individuals with subclinical hypothyroidism and symptoms consistent with mild hypothyroidism 6
Special Considerations
- Cardiovascular events may be reduced in patients under age 65 with subclinical hypothyroidism who are treated with levothyroxine 2
- Patients with cardiovascular risk factors may benefit from treatment, especially younger patients 3
- Caution is necessary when treating elderly subjects with levothyroxine, as it may be associated with iatrogenic thyrotoxicosis 2, 6
- Combined treatment with levothyroxine and liothyronine may be preferred in some hypothyroid patients who are dissatisfied with treatment, especially those with a polymorphism in type 2 deiodinase 2