From the Guidelines
High TSH with normal T4 indicates subclinical hypothyroidism, and treatment should be considered based on TSH levels, symptoms, and risk factors, with the goal of maintaining TSH within the normal range (0.4-4.5 mIU/L) to prevent progression to overt hypothyroidism and associated morbidity and mortality.
Key Considerations
- For TSH above 10 mIU/L, levothyroxine (synthetic T4) is typically recommended, starting at 25-50 mcg daily for most adults, with adjustments every 6-8 weeks based on TSH levels 1.
- For TSH between 4.5-10 mIU/L, treatment is considered if symptoms exist or if there are risk factors like positive thyroid antibodies, heart disease, or pregnancy 1.
- Regular monitoring is essential, with TSH checks every 6-12 months to prevent progression to overt hypothyroidism, which can occur at a rate of 2-5% per year 1.
- Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast, and separated from calcium, iron supplements, and certain medications by at least 4 hours to ensure proper absorption.
Risk Factors and Associations
- Subclinical hypothyroidism is associated with poor obstetric outcomes and poor cognitive development in children 1.
- Evidence for dyslipidemia, atherosclerosis, and decreased quality of life in adults with subclinical hypothyroidism in the general population is inconsistent and less convincing 1.
- People at higher risk for thyroid dysfunction include the elderly, postpartum women, those with high levels of radiation exposure (>20 mGy), and patients with Down syndrome 1.
From the Research
High TSH and Normal T4
- High TSH (thyroid-stimulating hormone) and normal T4 levels can be an indication of subclinical hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones to meet the body's needs 2.
- According to a study published in the Journal of Internal Medicine, treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L, as treatment does not improve symptoms or cognitive function if the TSH is less than 10 mIU/L 2.
- The diagnosis of subclinical hypothyroidism 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 goals are age-dependent, with a 97.5 percentile (upper limit of normal) of 3.6 mIU/L for patients under age 40, and 7.5 mIU/L for patients over age 80 2.
Causes and Treatment
- Autoimmune thyroiditis (AIT) is a common cause of hypothyroidism, and treatment involves replacing thyroid hormone deficiency with synthetic hormones 3.
- Levothyroxine monotherapy is the standard treatment for hypothyroidism, but some patients may have persistent symptoms despite normalisation of thyroid function tests biochemically 4.
- In some cases, combined treatment with levothyroxine and liothyronine may be preferred, especially for patients with a polymorphism in type 2 deiodinase 2.
Diagnosis and Management
- The diagnosis of hypothyroidism is typically made on biochemical grounds through serum thyroid function tests, and reference ranges for thyroid function tests are based on fixed percentiles of the population distribution 4, 5.
- However, there is increasing awareness of the need for more individualised reference intervals based on key factors such as age, sex, and special circumstances such as pregnancy 4.
- Ongoing symptoms despite levothyroxine treatment have led to some patients using liothyronine or desiccated thyroid extract, and there is intense debate around the treatment thresholds and treatment strategies for hypothyroidism 4.