Patient Preparation: Morning collection (7 a.m. to 10 a.m.) is preferred.

The Adrenocorticotropic Hormone (ACTH) test measures the level of ACTH in the blood, which helps regulate cortisol production by the adrenal glands. It is used to diagnose conditions related to adrenal or pituitary gland disorders, such as Addison's disease or Cushing's syndrome.

Preparation: Fasting is usually required, and the test is often done in the morning due to daily fluctuations in ACTH levels.