Peter Attia prefers blood tests over saliva tests for measuring hormones and cortisol.

“I did what's called a Dutch test, which is a test that looks at urine, dried urine, and measures cortisol and cortisol metabolites because I actually felt I was sort of hypercortisolemic. And at least on the two days that I did that test, I was not. And I had kind of low adrenal, low-ish total adrenal output, but totally normal levels of free cortisol, which is actually what matters.”