Advantages and disadvantages of different thyroid function tests
| Test | Advantages | Disadvantages | Preferred use |
|---|---|---|---|
| Thyrotropin (thyroid-stimulating hormone, TSH)7 | Sensitive to changes in thyroid hormone levels Useful in diagnosing primary and secondary hypothyroidism | Can be influenced by nonthyroid factors (eg, illness, medications) | Primary test for diagnosing hypothyroidism and monitoring thyroid hormone replacement therapy |
| Free thyroxine (T4)2,8 | More accurate reflection of thyroid hormone levels than total T4, less influenced by changes in binding proteins | Can be affected by protein-binding changes, especially in certain conditions (eg, pregnancy, liver disease) | Essential for assessing thyroid hormone status, especially in conditions affecting thyroid-binding proteins |
| Free triiodothyronine (T3)7,9 | More accurate reflection of thyroid hormone activity than total T3, less influenced by changes in binding proteins | Lower concentration, weaker protein binding, less precise measurement Often normal in early and mild hypothyroidism due to mostly peripheral conversion, especially in early hypothyroidism | Consider in specific clinical scenarios, such as suspected nonthyroid illness syndrome or hyperthyroidism |
| Thyroglobulin | Elevated levels may indicate residual or recurrent thyroid cancer | Can be affected by thyroid inflammation and other factors | Used in the management of patients with thyroid cancer |
| Thyroid peroxidase antibodies | Positive test suggests autoimmune thyroiditis; often associated with Hashimoto thyroiditis | Not specific—can be positive in other autoimmune conditions | Used in the diagnosis and management of autoimmune thyroid diseases |