This is what I remember of the test given to my daughter at 3 years of age. She was put in the hospital for the day and the test was administered by an endocrinologist and a nurse.at The ACTH stimulation test is done over several hours and requires an IV. ACTH stands for adrenocorticotropic hormone and is produced in the pituitary gland. When released, ACTH stimulates the adrenal to produce cortisone. The adrenals also produce salt retaining hormones and androgens (progesterone) In a simplified version, An IV is hooked up and base sample of blood is taken. A controlled amount of a substance which acts like ACTH is injected through the IV. After ½ hr a second blood sample is taken. A total of approx 3 - 4 more samples are taken at half hour intervals. The change in levels of 17a-hydroxyprogesterone is what is being measured. The results show whether the adrenal glands are functioning normally. Note: the IV may sound scary but it sure beat having a new needle each time another blood sample was taken. This test would be comparable to testing a person for diabetes and seeing if there is any change in the levels of insulin. From what I understand, there are varying levels of this disorder (CAH). It turns out that my daughter is able to produce minute amounts of cortisone, but certainly not enough to sustain normal growth and normal immune response. When these test results came back, it showed severely high levels of the progesterone. She was diagnosed with non-salt losing CAH. Salt losers are more likely to have an adrenal crisis than salt losers. Even so, I think she was fortunate not to have any major illness such as a broken bone, chicken pox or pneumonia before she was diagnosed. We still monitor her very closely when she is ill. I’m sure if I dug further into my files I could get you more detailed info but I’m sure an endo would certainly explain this. There may be some newer technologies available since my daughter had this done in 1988. Please note, my daughter had numerous types of tests done prior to this one. They all showed normal levels. Hope this info helps.