In cases of suspected Cushing's disease, which test is crucial for evaluating the functionality of the pituitary gland?

In cases of suspected Cushing's disease, measuring the adrenocorticotropic hormone (ACTH) level is crucial for evaluating the functionality of the pituitary gland. Cushing's disease specifically refers to the excess production of cortisol due to an ACTH-secreting pituitary adenoma. By assessing the ACTH levels, healthcare providers can differentiate between various causes of Cushing's syndrome, including whether the condition is pituitary (Cushing's disease) or due to adrenal tumors or ectopic ACTH production.

If ACTH levels are elevated, this suggests a potential pituitary cause of cortisol overproduction. Conversely, low or undetectable ACTH levels indicate that the adrenal glands may be producing excess cortisol autonomously, which occurs in cases of adrenal tumors. Recognizing these distinctions guides further diagnostic testing and management, making ACTH measurement a critical step in evaluating pituitary functionality in suspected Cushing's disease.