Cortisol is produced by your adrenal glands that can have an impact on how your body uses thyroid. Doctors are supposed to make sure everything is good with your adrenal glands before even putting you on thyroid meds so it is good they are checking it (it's even notated on thyroid Rx info that you should rule out/resolve adrenal issues prior to taking thyroid medication). Sometimes some of the symptoms between adrenal issues and thyroid issues can overlap so its good to rule out any problems there. Docs want to test first thing in the morning b/c it has a circadian rhythm that peaks in the morning. If it's really low or way too high in the am then it shows your adrenals may not be functioning correctly. The blood test is okay but the best way to test your cortisol is actually through saliva sampling. It tests 4 times throughout the day to see what your adrenals are doing throughout the day instead of just in the morning. This test is not covered by any insurance companies though I don't believe as it is still not considered a good test by most conventional docs but it does seem to be gaining recognition as a reliable test more and more by the medical community. Hope this info was able to answer your question. Good luck!
Cortisol is best checked at 8am-ish, because that is when our cortisol levels are at they are at their highest
Cortisol levels begin to peak in the early morning to wake up up.
Cortisol levels drop throughout the day and are lowest at bedtime so we can fall asleep.
The following is from labtestsonline.com
In normal people, cortisol levels are very low at bedtime and at their highest just after waking. This pattern will change if a person works irregular shifts (such as the night shift) and sleeps at different times of the day. With Cushing’s syndrome, this pattern is typically lost.
Increased or normal cortisol concentrations in the morning along with levels that do not drop in the afternoon and evening suggest an overproduction of cortisol. If this excess cortisol is suppressed during a dexamethasone suppression test, it suggests that the excess cortisol is due to increased pituitary ACTH production. If it is not suppressed, then the increased cortisol could be due to an ACTH-producing tumor outside of the pituitary, due to a problem with the adrenal gland, or due to a medication that the patient is taking.
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