From the Guidelines
For a hyperthyroid workup, start with a thyroid-stimulating hormone (TSH) test and free T4 level, as recommended by the USPSTF 1. If TSH is low and free T4 is high, hyperthyroidism is confirmed. Next steps include:
- Free T3 level
- Thyroid antibodies (TSI, TPO, TRAb)
- Radioactive iodine uptake scan
- Thyroid ultrasound Additional tests may include:
- Complete blood count
- Liver function tests
- Calcium level Consider testing for Graves' ophthalmopathy if eye symptoms are present. Treatment options depend on the cause but may include:
- Antithyroid medications (methimazole 10-30 mg daily or propylthiouracil 100-300 mg daily)
- Beta-blockers (e.g., propranolol 20-40 mg 3-4 times daily) for symptom control
- Radioactive iodine therapy
- Thyroidectomy in select cases Monitor thyroid function every 4-6 weeks initially, then every 3-6 months once stable, as there is no direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes 1. This approach helps identify the cause of hyperthyroidism (e.g., Graves' disease, toxic nodular goiter) and guides appropriate treatment, with the goal of improving morbidity, mortality, and quality of life. The combination of tests provides a comprehensive picture of thyroid function and structure, enabling targeted therapy, and is in line with the USPSTF recommendation statement 1.
From the FDA Drug Label
Once clinical evidence of hyperthyroidism has resolved, the finding of a rising serum TSH indicates that a lower maintenance dose of methimazole should be employed. Thyroid function tests should be monitored periodically during therapy
The diagnosis of hyperthyroidism is based on clinical evidence and thyroid function tests, including serum TSH levels.
- Thyroid function tests should be monitored periodically during therapy to assess the patient's response to treatment.
- A rising serum TSH level may indicate that the patient's hyperthyroidism has resolved, and a lower maintenance dose of methimazole may be necessary 2.
From the Research
Diagnosis of Hyperthyroidism
Hyperthyroidism, also known as an overactive thyroid gland, can be diagnosed through a combination of clinical presentation, thyroid function tests, and thyrotropin-receptor antibody status 3. The diagnosis of hyperthyroidism is typically established based on:
- Suppressed thyrotropin (previously thyroid-stimulating hormone) and high concentration of triiodothyronine (T3) and/or free thyroxine (FT4) for overt hyperthyroidism
- Low concentrations of thyrotropin and normal concentrations of T3 and FT4 for subclinical hyperthyroidism
Clinical Assessment and Laboratory Tests
Clinical assessment of the patient with suspected thyroid disease remains an important part of the workup 4. Available laboratory tests of thyroid function include:
- Measurements of serum thyroid hormones and thyroid-stimulating hormone
- Titers of autoantibodies involved with Graves' disease and thyroiditis
- Thyroid imaging and uptake techniques
Subclinical Hyperthyroidism
Subclinical hyperthyroidism is a biochemical diagnosis characterized by a decreased serum thyroid-stimulating hormone (TSH) and normal serum thyroxine (T4) and triiodothyronine (T3) concentrations 5. Proposed grading systems distinguish between mild and severe subclinical hyperthyroidism and are used alongside patients' age and the presence of risk factors and symptoms to guide treatment.
Method Differences in Free Thyroid Hormone Assays
Free T4 (FT4) determination is one of the most commonly performed biochemical tests in endocrinology, and treatment of thyroid dysfunctions is adjusted based on the severity of symptoms and biochemical test results 6. However, large non-linear method differences at high FT4 concentrations can affect assessment of hyperthyroid status, and clinicians should be aware of these differences when interpreting results.
Laboratory Testing in Thyroid Conditions
Thyroid disorders are common, and laboratory tests are integral in the management of these conditions 7. The repertoire of thyroid tests includes blood tests for thyroid-stimulating hormone (TSH), free thyroxine, free triiodothyronine, thyroglobulin (Tg), thyroglobulin antibodies (Tg-Ab), thyroid peroxidase antibodies (TPO-Ab), TSH receptor antibodies (TRAb), and calcitonin. Clinicians and laboratorians should be mindful of possible assay interferences and/or the effects of concurrent medications when interpreting results.