From the Guidelines
The diagnosis of hyperthyroidism typically requires TSH levels below 0.1 mIU/L, with free T4 and/or free T3 levels above the normal range, as treatment is generally recommended for patients with a TSH level that is undetectable or less than 0.1 mIU/L, particularly those with overt Graves disease or nodular thyroid disease 1.
Key Considerations
- The severity of hyperthyroidism can be categorized based on TSH levels, with Grade 1 having TSH between 0.1-0.4 mIU/L and Grade 2 having TSH below 0.1 mIU/L.
- Normal reference ranges for free T4 and free T3 vary slightly between laboratories, but typically free T4 ranges from 0.7-1.9 ng/dL and free T3 from 2.3-4.2 pg/mL.
- Treatment decisions depend on both the laboratory values and clinical symptoms, with more aggressive intervention typically recommended for those with completely suppressed TSH and elevated thyroid hormones, especially when accompanied by significant symptoms like tachycardia, weight loss, or tremor.
Diagnostic Approach
- The serum TSH test is the primary screening test for thyroid dysfunction, with multiple tests done over a 3- to 6-month interval to confirm or rule out abnormal findings.
- Follow-up testing of serum T4 levels in persons with persistently abnormal TSH levels can differentiate between subclinical and overt thyroid dysfunction.
- Additional tests like thyroid antibodies, thyroid uptake scans, and ultrasound may be necessary to determine the underlying cause of hyperthyroidism.
Treatment
- Hyperthyroidism is treated with antithyroid medications or nonreversible thyroid ablation therapy, with the choice of treatment depending on the underlying cause and severity of the disease.
- Treatment is typically not recommended for patients with TSH levels between 0.1 and 0.45 mIU/L or when thyroiditis is the cause, as these patients are unlikely to progress to overt hyperthyroidism 1.
From the Research
Cut-off Values for Thyroid Function Tests in Hyperthyroidism
- The cut-off values for thyroid function tests in hyperthyroidism are as follows:
- Specifically, subclinical hyperthyroidism can be further divided into two grades:
- A chemiluminescent TSH assay with a detection limit of less than 0.01 mU/L can accurately measure subnormal TSH concentrations 4
- Treatment for subclinical hyperthyroidism is recommended for patients 65 years or older with TSH levels lower than 0.10 mIU/L, symptomatic patients, or those with cardiac or osteoporotic risk factors 2
- The use of radioiodine therapy is considered a treatment of choice for patients with nodular goiter 5