ACTH levels in the blood are measured to help detect, diagnose, and monitor conditions associated with excessive or deficient cortisol in the body. These conditions include:

Cushing’s disease: excess cortisol that is due to an ACTH-producing tumor in the pituitary gland (usually a benign tumor)

Cushing's syndrome: refers to the symptoms and signs associated with excess exposure to cortisol. In addition to Cushing’s disease, Cushing’s syndrome may be due to an adrenal tumor, adrenal hyperplasia (increased adrenal cell growth), the use of steroid medications, or due to an ACTH-producing tumor that is located outside the pituitary (such as in the lungs).

Addison's disease, primary adrenal insufficiency: decreased cortisol production due to adrenal gland damage

Secondary adrenal insufficiency: decreased cortisol production because of pituitary dysfunction

Hypotituitarism: pituitary dysfunction or damage that leads to decreased (or no) hormone production by the pituitary – including ACTH production

Measuring both ACTH and cortisol can help to differentiate among some of these conditions. Because the level of ACTH normally changes in the opposite direction to the level of cortisol, your doctor can learn much by identifying an imbalance in this relationship and the direction in which the imbalance occurs. The table below indicates the common patterns of ACTH and cortisol seen with different diseases involving the adrenal and pituitary glands.