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Fast for serum cortisol
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Fast for serum cortisol

I am confused. I've read in several lab manuals that you don't need to fast for a morning serum cortisol. Then I've read you should fast for at least 2 to 3 hours before the test. But I've also read you should fast for 12 hours.

So, my question is, how will cortisol be affected if you fast versus if you don't fast?

Will cortisol be higher or lower with food?  

It kind of makes me wonder about testing at all when my endocrinologist doesn't believe stress can influence a cortisol level, but food can. ???
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657231_tn?1453836403
My better docs have always insisted on fasting. My one doc wants a 12 hour fast. Another , 8,

I don't know - I have always fasted for my tests, for years. But not the salivary ones...

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Do you know if the results of serum cortisol would be expected to be higher or lower with food (non-fasting)?

And/or does it really matter?

If 24 hr UFC,  midnight salivary swab, and serum cortisol measurements taken in the afternoon and evening do not consider fasting versus non-fasting, is it that important to obtain an 8am serum cortisol after fasting?  

But I'm mostly curious if non-fasting would skew the 8am serum higher or lower?

thanks again for your information.

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657231_tn?1453836403
I don't know - except that my docs think it matters and I do it generally with a whole bunch of other tests so I make sure I am fasting?

Serum is different than free - free has other pitfalls. Point in time vs averages etc.

If it is mandated, it must make some sort of difference - that one I have not tested on myself LOL... but have no researched either.
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