Low cortisol levels indicate adrenal fatigue. They test cortisol levels with a saliva test at 4 different times throughout any chosen day. Hopefully, I'm explaining this correctly, but if your cortisol levels are unusually low first thing in the morning (when they should be at their highest), this indicates adrenal fatigue. I got the saliva test from my naturopath, but I've seen other posts on here where people were buying them online and in pharmacies? She also tested my urine and did blood tests, but the saliva test gives cortisol levels. Hope that helps.