Corticorelin is a diagnostic agent. It is a corticotropin-releasing hormone

Corticotropin-releasing hormone

Corticotropin-releasing hormone , originally named corticotropin-releasing factor , and also called corticoliberin, is a polypeptide hormone and neurotransmitter involved in the stress response...

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The corticorelin stimulation test helps to differentiate between the etiologies of ACTH-dependent hypercortisolism. It is used to evaluate the status of the pituitary-adrenal axis in the differentiation of a pituitary source from an ectopic source of excessive ACTH secretion.

• If corticorelin injection increases plasma levels of ACTH and cortisol, a diagnosis of Cushing's disease
  Cushing's disease
  Cushing's disease is a cause of Cushing's Syndrome characterised by increased secretion of adrenocorticotropic hormone from the anterior pituitary. This is most often as a result of a pituitary adenoma...
  
   is achieved (ACTH of pituitary origin).
• If corticorelin injection leads to little or no response in plasma levels of ACTH or cortisol, a diagnosis of Ectopic ACTH syndrome is confirmed.