Adrenocorticotropic hormone (ACTH) is a peptide hormone produced by the anterior pituitary gland. It plays a crucial role in stimulating the adrenal glands to release cortisol, a hormone involved in stress response, metabolism, blood pressure regulation, and immune response.

A plasma ACTH test measures the concentration of ACTH in your blood to help diagnose or monitor conditions related to the adrenal or pituitary glands. It is often ordered when a doctor suspects issues such as:

• Cushing's disease or syndrome: A condition involving excess cortisol production.
• Addison's disease: A condition involving inadequate cortisol production.
• Secondary adrenal insufficiency: Where ACTH production is insufficient due to pituitary gland dysfunction.

Interpretation of Results:

• High ACTH levels can indicate primary adrenal insufficiency (Addison's disease) or ectopic ACTH production (such as in certain tumors).
• Low ACTH levels may be seen in cases of adrenal hyperfunction, such as Cushing's syndrome due to an adrenal tumor, or in secondary adrenal insufficiency.

For accurate assessment, ACTH levels are often measured alongside cortisol levels to provide a clearer picture of adrenal and pituitary function. The test typically requires a blood sample drawn in the morning when ACTH levels are at their peak.