Question: I had low estrogen (age 33) and was referred to an endocrinologist. I asked to be tested for Cushing’s. I was scheduled for an insulin tolerance test, but ended up having a glucagon test. I was told that all of my hormones, including cortisol, were normal. Are these tests ever used to diagnose Cushing’s? 

Answer: The 3 screening tests for Cushing’s syndrome are (1) 24 hour urine free cortisol, (2) midnight salivary cortisol levels, (3) 1 mg overnight dexamethasone suppression test. All are equally reliable in screening for Cushing’s (approximately 92% accurate). A patient may have a “normal” blood cortisol test and still have Cushing’s — a single cortisol is not a diagnostic test for Cushing’s. The glucagon test is used to determine if a patient has growth hormone deficiency.

By Dr. Mary Lee Vance, MD, Professor of Medicine and Neurosurgery, University of Virginia, Spring, 2017