Which test is considered the best screening test for thyroid function?

The best screening test for thyroid function is TSH, or Thyroid Stimulating Hormone. This test measures the level of TSH in the blood, which is produced by the pituitary gland to regulate the production of thyroid hormones (T3 and T4) by the thyroid gland itself.

TSH is highly sensitive to even slight changes in thyroid hormone levels; therefore, it serves as a reliable indicator of thyroid function. When the thyroid is underactive (hypothyroidism), TSH levels typically increase as the body tries to stimulate the thyroid to produce more hormones. Conversely, when the thyroid is overactive (hyperthyroidism), TSH levels tend to decrease due to feedback mechanisms. This makes TSH the first-line test for assessing thyroid health in individuals.

The other tests mentioned, such as Free T4, thyroid scans, and thyroid antibodies, are valuable in specific contexts but are not typically used as initial screening tests. Free T4, for instance, provides information about the level of thyroxine in the blood but does not reflect the regulatory function of the thyroid as effectively as TSH. Thyroid scans assess anatomical abnormalities or the functional state of the thyroid but are not designed for general thyroid function screening. Thyroid antibodies tests are