What is the best screening test for detecting thyroid disorders?

The thyroid-stimulating hormone (TSH) test is considered the best initial screening test for detecting thyroid disorders because it is highly sensitive and specific for assessing thyroid function. TSH is produced by the pituitary gland and regulates the production of thyroid hormones (T3 and T4) by the thyroid gland. When thyroid hormone levels are low, TSH levels will rise in an attempt to stimulate the thyroid gland to produce more hormones. Conversely, when thyroid hormone levels are high, TSH levels will fall.

Because of this feedback mechanism, TSH is an excellent marker for identifying both overt and subclinical thyroid dysfunction. A high TSH level often indicates hypothyroidism, while a low TSH level is suggestive of hyperthyroidism. In practice, TSH testing is typically the first step in assessing thyroid function because it provides a clear indication of the thyroid's health without the need for more complex assessments initially.

The other options do not serve as effective standalone screening tests. Total T3 and T4 can vary based on several factors and may not accurately reflect thyroid function without TSH levels. A thyroid profile, which could include TSH, T3, and T4, is more comprehensive but is not typically used as an initial screening tool