From the Guidelines
The initial step in evaluating thyroid function is measuring thyroid-stimulating hormone (TSH) levels, which serves as the most sensitive screening test for thyroid dysfunction. If TSH is abnormal, subsequent testing typically includes free thyroxine (T4) and sometimes free triiodothyronine (T3) to determine the specific thyroid disorder.
Key Considerations
- For hypothyroidism, treatment involves levothyroxine replacement therapy, usually starting at 1.6 mcg/kg/day (typically 50-100 mcg daily for adults), with dose adjustments every 6-8 weeks based on TSH levels until reaching the target range of 0.5-2.5 mIU/L 1.
- For hyperthyroidism, treatment options include anti-thyroid medications like methimazole (starting at 10-30 mg daily) or propylthiouracil (100-300 mg daily in divided doses), radioactive iodine ablation, or thyroidectomy 1.
- Beta-blockers such as propranolol (20-40 mg 3-4 times daily) may be used initially to control symptoms like tachycardia and tremors.
- Regular monitoring is essential for all thyroid disorders, with TSH checks every 6-12 months after stabilization.
- Thyroid function testing should be performed in the morning, before taking thyroid medication, and patients should be advised that many medications and supplements can interfere with thyroid function or medication absorption.
Treatment Approach
- The principal treatment for hypothyroidism is oral T4 monotherapy (levothyroxine sodium) 1.
- Hyperthyroidism is treated with antithyroid medications or nonreversible thyroid ablation therapy (for example, radioactive iodine or surgery) 1.
Special Considerations
- Patients with previously normal TSH levels may be rechecked every 1–2 years or obtained at any time the growth rate is abnormal 1.
- The presence of thyroid autoantibodies (antithyroid peroxidase [TPO] and antithyroglobulin [TG]) identifies patients at increased risk for thyroid autoimmunity 1.
From the FDA Drug Label
The diagnosis of hypothyroidism is confirmed by measuring TSH levels using a sensitive assay (second generation assay sensitivity ≤ 0. 1 mlU/L or third generation assay sensitivity ≤ 0. 01 mlU/L) and measurement of free-T4. The initial step in evaluating thyroid function is to measure TSH levels and free-T4.
- Subsequent tests may include:
- Serum T4 levels
- Total- or free-T4
- Treatments for thyroid disorders include:
- Levothyroxine replacement therapy
- Monitoring of TSH and free-T4 levels to adjust the dose of levothyroxine as needed
- Regular physical examinations and laboratory tests to assess the adequacy of therapy and detect any potential complications 2
From the Research
Initial Evaluation of Thyroid Function
- The initial step in evaluating thyroid function is to measure the thyroid-stimulating hormone (TSH) level, which is the preferred test for initial evaluation of suspected primary hypothyroidism 3.
- If TSH is abnormal, a free thyroxine (T4) level will further narrow the diagnosis.
- Obtain a triiodothyronine (T3) level if TSH is undetectable and free T4 is normal.
Subsequent Tests for Thyroid Disorders
- TSH and free thyroid hormone tests are frequently used to assess the functional status of the thyroid 4.
- Thyroid peroxidase antibodies (TPO-Ab) and TSH receptor antibodies (TRAb) tests are used to diagnose Hashimoto's thyroiditis and Graves' disease, respectively 4.
- Thyroglobulin (Tg) and calcitonin are important tumor markers used in the management of differentiated thyroid carcinoma and medullary thyroid carcinoma (MTC), respectively 4.
Treatment of Thyroid Disorders
- Treatment options for overt hyperthyroidism from autonomous thyroid nodules or Graves disease include antithyroid drugs, radioactive iodine ablation, and surgery 5.
- Treatment for subclinical hyperthyroidism is recommended for patients at highest risk of osteoporosis and cardiovascular disease, such as those older than 65 years or with persistent serum thyrotropin level less than 0.1 mIU/L 5.
- Long-term methimazole treatment was superior to radioiodine therapy in patients with diffuse toxic goiter when mood, cognition, cardiac function, and occurrence of thyroid dysfunction were compared 6.