CRH Test

This test can be used to distinguish between pituitary-dependent Cushing's and ectopic source of Cushing's. CRH is administered intravenously and the cortisol response monitored. Normally there is a rise in both ACTH and cortisol. In pituitary-dependent Cushing's patients the response is exaggerated, and in ectopic ACTH syndrome there will be no response.