Which diagnostic test would typically be ordered to assess thyroid function?

The diagnostic test commonly ordered to assess thyroid function is the Thyroid-Stimulating Hormone (TSH) test. TSH is produced by the pituitary gland and stimulates the thyroid gland to produce thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3). By measuring the level of TSH in the blood, healthcare providers can gain insight into how well the thyroid is functioning.

High levels of TSH may indicate hypothyroidism, where the thyroid is underactive, while low levels may suggest hyperthyroidism, indicating an overactive thyroid. The TSH test is typically the first step in the evaluation of thyroid disorders as it provides critical information about the feedback mechanism between the pituitary gland and the thyroid gland, making it a vital tool in diagnosing conditions related to thyroid function.

Other tests mentioned, such as a complete blood count, B-type natriuretic peptide, and electrolytes, serve different diagnostic purposes and do not directly assess thyroid function. A complete blood count evaluates overall health and detects various conditions, B-type natriuretic peptide is used to evaluate heart failure, and electrolyte tests assess the balance of minerals in the body, none of which provide specific information about thyroid function.