Which test is commonly used for diagnosing Addison's disease?

The ACTH stimulation test is a key diagnostic tool for determining the presence of Addison's disease, which is characterized by insufficient production of cortisol due to adrenal gland dysfunction. In this test, synthetic adrenocorticotropic hormone (ACTH) is administered, and the body's response is measured through subsequent cortisol levels. In individuals with Addison's disease, there is a blunted or absent cortisol response to the ACTH administration, which confirms the diagnosis.

The other tests listed provide useful information regarding adrenal function but are not specific for diagnosing Addison's disease. For instance, the ACTH suppression test assesses the feedback mechanism of cortisol but is typically used for conditions like Cushing's syndrome. The 24-hour urinary cortisol test measures the total cortisol excretion over a day and is primarily used for diagnosing conditions with excess cortisol production rather than underproduction, like in Addison's disease. Finally, the insulin tolerance test evaluates the adrenal reserve by inducing hypoglycemia to stimulate cortisol release, but it is considered less safe and not routinely employed for diagnosing adrenal insufficiency. Thus, while these other tests have their roles in evaluating adrenal function, the ACTH stimulation test is the most direct and specific for Addison's disease.