About three months ago I was seen at the Mayo Clinic in Rochester for extreme fatigue. They found that my cortisol was low, a 5.8 with a reference range of 7-20 (the blood was taken at 10am). I was told to follow up with my regular doctor in three months, which I just did, to have another cortisol test. My doctor said if it came back low again I would be referred to an endocrinologist. This time it came back a 4.8, even lower than last time. Blood was drawn at 8:30am. However, I just got a letter from my doctor saying my cortisol looks like it’s back within normal range, with the reference range listed at 4.8-20. Can someone maybe explain to me how the reference range changed? This isn’t me being sarcastic, I genuinely want to know how the reference range could change like that. I know cortisol levels vary throughout the day but I was told they are supposed to be highest that early in the morning or something like that. I’m too afraid to ask my doctor about it because I have gone through so many doctors now trying to figure out what is wrong and I don’t want my doctor to think I’m a hypochondriac or something so I figured I would ask here. Thank you in advance to anyone who can give me any info on this!