I receive e-mails from patients who have already received a diagnosis of hypothyroidism and are being treated for it. They also suspected they might be suffering from co-morbid (co-occurring) Adrenal Fatigue and relate this to their Doctors. Their Doctors will usually order them a blood test of their blood cortisol level (major adrenal hormone) and they (patients) will ask me if I feel this is a good test for Adrenal Fatigue or Adrenal Insufficiency. I usually express to them that in my opinion the blood test needs to be the one called the "ACTH Stimulation Test", also called the "Cortrosyn Stimulation Test", which can rule out or confirm true Adrenal Insufficiency but I also point out that saliva testing done at multiple times during a 24 hour period, can also detect a low cortisol rhythm as well, such as that which manifests in adrenal fatigue. I will also mention to them that a single blood draw of cortisol levels, is like a snapshot reading and doesn't establish how the cortisol rhythm is functioning throughout the day.
A single blood draw, of cortisol, is like a snapshot reading, so doesn't really establish what your cortisol rhythm is doing. A better test of adrenal function is the "ACTH Stimulation Test", which takes a baseline reading then two more at thirty minute intervals, after giving the patient an injection of the ACTH hormone (the one that stimulates cortisol production). They want to see a significant increase in cortisol with the two stimulated readings and if there isn't an adequate increase, they may diagnose adrenal insufficiency.
There are also saliva cortisol tests available that establish your cortisol circadian rhythm because these test kits contain tubes to collect samples at 3 or 4 different times during a 24 hour period. These are not terribly expensive and a lot less expensive than an ACTH Stim Test but may not matter if you have insurance that covers all of your diagnostic tests. Many pharmacies carry the saliva ones, usually the "ZRT Labs, Inc." brand, so you might check with your local pharmacy. If they do not carry them, ZRT tests are available online.
The National Institutes of Health and the World Health Organization, recognize saliva cortisol testing as being very accurate. Major insurance providers also recognize saliva cortisol testing, including the Blue Shield Company.
Articles on the National Institutes of Health "PubMed" website and others from the Endocrine Society state clearly, that there is accuracy and convenience in saliva cortisol testing.
These are the reasons I believe saliva cortisol testing is the best method for detecting adrenal fatigue, once a patient has had full-blown adrenal insufficiency ruled out via an ACTH Stimulation test.