From the Guidelines
Elevated Thyroid-Stimulating Hormone (TSH) and decreased Free Thyroxine (FT4) levels indicate primary hypothyroidism, which requires thyroid hormone replacement therapy to prevent long-term complications and improve quality of life. The primary goal of treatment is to normalize TSH levels and alleviate symptoms. According to the most recent guidelines 1, patients with elevated TSH levels (>10 mIU/L) and decreased FT4 levels should be treated with thyroid hormone supplementation, regardless of symptoms.
Treatment Approach
- The starting dose of levothyroxine is typically based on weight and age, approximately 1.6 mcg/kg/day for otherwise healthy adults, but lower (25-50 mcg/day) for elderly patients or those with heart disease 1.
- Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast or 3-4 hours after the last meal of the day, and separated from other medications, vitamins, or supplements containing calcium, iron, or magnesium by at least 4 hours.
- After starting treatment, TSH levels should be checked every 6-8 weeks, with dose adjustments as needed until levels normalize 1.
- Once stable, annual monitoring is typically sufficient.
Monitoring and Follow-up
- TSH and FT4 levels should be monitored regularly to assess the effectiveness of treatment and adjust the dose as needed 1.
- Patients with severe symptoms or life-threatening consequences should be hospitalized and treated with intravenous levothyroxine and supportive care 1.
Causes and Risk Factors
- Common causes of primary hypothyroidism include Hashimoto's thyroiditis, iodine deficiency, and previous thyroid surgery or radiation treatment 1.
- Risk factors for elevated TSH levels include female sex, advancing age, white race, type 1 diabetes, Down syndrome, family history of thyroid disease, and previous hyperthyroidism 1.
From the Research
Implications of Elevated TSH and Decreased FT4
- Elevated Thyroid-Stimulating Hormone (TSH) and decreased Free Thyroxine (FT4) levels can indicate hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones 2, 3.
- In patients with central hypothyroidism, elevated TSH and decreased FT4 levels can be used to diagnose the condition, but the diagnosis is often reached by measuring TSH and FT4 concentrations together 2.
- Patients with pituitary disease are at risk of under-replacement with levothyroxine, and achieving optimal thyroid hormone replacement is more difficult in TSH deficiency compared to primary hypothyroidism 3.
- TSH levels may not be a good marker for adequate thyroid hormone replacement therapy, as patients with T4-treated hypothyroidism can have lower T3 levels and lower SHBG than normal individuals with the same TSH levels 4.
Thyroid Hormone Replacement Therapy
- Levothyroxine replacement therapy should be established taking into account the weight, age, and presence of other hormone deficiencies or pharmacological treatment of patients 2.
- The L-T4 daily dose should be adjusted to achieve normal FT4 and FT3 serum levels, and some biochemical indexes of thyroid hormone action are necessary to accurately disclose over- or undertreated patients 2, 5.
- Mild TSH suppression with LT4 may be needed to achieve normal FT3 levels in patients with atrophic thyroid glands after radioiodine treatment for Graves' disease 5.
Limitations of TSH Measurements
- TSH measurements alone may be sufficient for screening and monitoring L-T4 replacement or suppression therapy if TSH levels are above 0.05 mU/L, but may be misleading in pituitary disease and during the treatment of hyperthyroidism 6.
- Knowledge of FT4 is necessary if TSH levels are less than 0.05 mU/L to assess the degree of hyperthyroidism, and TSH alone is not sufficient for the diagnosis or follow-up of central hypothyroidism patients 2, 6.