What test is indicated in a patient showing symptoms of adrenal insufficiency?

In a patient exhibiting symptoms of adrenal insufficiency, the adrenocorticotropic hormone (ACTH) stimulation test, also known as the ACTH stimulation test or cosyntropin stimulation test, is the most appropriate and relevant test to confirm the diagnosis. This test assesses the adrenal glands' ability to produce cortisol in response to stimulation by ACTH.

In cases of primary adrenal insufficiency, such as Addison's disease, the adrenal glands fail to produce adequate cortisol despite stimulation by ACTH. The result of the test typically shows inadequate cortisol production, which allows for the confirmation of adrenal insufficiency. In contrast, secondary adrenal insufficiency, often due to insufficient ACTH production from the pituitary gland, will show a response to ACTH stimulation, highlighting the distinction between primary and secondary causes of adrenal insufficiency.

The other tests listed do not provide direct insight into adrenal function. Thyroid function tests evaluate thyroid hormone levels and are unrelated to adrenal function. Fasting blood sugar measures glucose levels, which is more pertinent for assessing metabolic conditions rather than adrenal insufficiency. A complete blood count provides information about overall health and can indicate conditions such as anemia or infection but does not specifically address adrenal hormone levels or function. Therefore, the ACTH stimulation test is