Diagnostic procedures that measure the performance of the thyroid gland. These tests detect hyperthyroidism (overactivity of the thyroid gland) or hypothyroidism (underactivity of the thyroid gland), and the tests include blood tests and thyroid scanning procedures.
A test for evidence of increased or decreased thyroid function, including a clinical physical examination, which is usually reliable, and a variety of reliable laboratory tests. The most commonly used test to assess thyroid function is the measurement of thyroid-stimulating hormone (TSH) with supersensitive assays. Usually, TSH levels are high in hypothyroidism and suppressed in hyperthyroidism, although in patients with pituitary masses this pattern may be reversed. Other thyroid function tests include measurements of free and total thyroxine (T4) and triiodothyronine (T3), tests of thyroid-binding globulin levels, antithyroid antibody tests, and thyroid gland radioactive iodine uptake (RAIU) measurement. Many of these test results are more difficult to interpret than are TSH results because their normal ranges may vary with pregnancy, liver disease, nutritional status, and other medical conditions.