Vic,
They can test both ACTH and cortisol level by blood. Years ago when I was getting adrenal testing my then-doctor was first going to have my ACTH and cortisol tested and explained the same thing to me about ACTH going high when its trying to stimulate the adrenal glands if they are hypofunctioning. He instead ordered me the ACTH Stim Test but mine was normal although my starting level (baseline) was lowest normal (adrenal fatigue). I also had a 24 hour urinary cortisol test (usually used to detect elevated cortisol) that was also very low normal result. The low-normals aren't recognized by most doctors as meaning anything. They want to see absolute full blown adrenal insufficiency and won't diagnose subclinical forms of adrenal insufficiency even though they do diagnose subclinical hypothyroidism, borderline diabetes etc...
If you have low-normal adrenal fiunction this will be strong indication of adrenal fatigue. Studies by the U.S.Gov/NIH and other reputable organizations have found consistently low-normal cortisol in conditions like Chronic Fatigue Syndrom, Post Traumatic Stress Disorder and Fibromyalgia but they won't refer to it as adrenal fatigue. They will call it mild adrenal insufficiency or hypocortisolemia.
It's also possible you have comorbid CFS as I do. Mine manifests mostly with muscle weakness and post exertion malaise (bad reaction to physical extertion and long recovery time). If this does happen to be the case, don't let that overly concern you because many people recover in 2 to 5 years from CFS (some sooner) and those who have it longer term, as I do, can do things and their doctors can offer treatments to help with symptoms. Some thyroid patients see CFS and FMS (fibromyalgia) resolve over time with thyroid hormone treatment alone.
Keep us posted on the MG and other test results!