Which lab test is used to evaluate thyroid function?

The thyroid-stimulating hormone (TSH) test is the primary laboratory test used to evaluate thyroid function. It helps assess how well the thyroid gland is working by measuring the level of TSH in the blood, which is produced by the pituitary gland. TSH plays a critical role in regulating the production of thyroid hormones (T3 and T4) from the thyroid gland itself. Elevated levels of TSH typically suggest an underactive thyroid (hypothyroidism), while low levels indicate an overactive thyroid (hyperthyroidism).

In contrast, a complete blood count (CBC) assesses general health and detects a variety of disorders, but it does not provide specific information about thyroid function. Similarly, a lipid panel measures cholesterol and triglyceride levels, while a basic metabolic panel (BMP) evaluates electrolyte balance, kidney function, and blood glucose levels. Neither of these tests offers insights into the functioning of the thyroid gland, making the TSH test the most pertinent choice for assessing thyroid function.