Does anyone know which is more accurate? An ACTH or saliva testing for the cortisol levels, someone did tell me that just drawing a tube of blood twice a day to check the cortisol is not accurate at all?? Thanks
They are not the same.
It is my opinion and if you read up, that more testing is better, as well as time of day is critical.
As for ACTH and cortisol, ACTH is akin to a radio signal while cortisol is a radio receiver. They both need to work. Testing both tells what is the issue - the tower or the radio. The radio, the adrenals, has a cycle, the diurnal rthym, so you must test at the right times to know when cortisol normally peaks or ebbs.
As for saliva, that is the free type. There are some people that have high cortisol binding globulin and will not spill free cortisol and so those tests are not accurate. Urine tests would be the same. Estrogen (androgens) interfere with the free type tests as well as other medications and may interfere with the serums as well.
ACTH is also fussy, and degrades at room temp so handling by the lab tech after draw is critical - they must spin it as soon as possible to get the most accurate reading. The tube should be chilled but only a few labs do that.
I fast for my morning tests. My one doctor specifies a 12 hour fast and wants the test off medications. Your doctor should tell you. I get a lot of tests besides ACTH, and so maybe I am fasting for other ones - but overall, I am fasting.
My son is having a repeat synacthen test next month. The hospital have told us to omit the afternoon/evening dose the day before the test and the morning dose on test day. He is on hydrocortisone which, so I am told, doesn't stay in the system long. I am not sure when you would have to stop if you were taking prednisone which is longer acting.
If you are told to omit a dose, you can do so, usually safely, but contact the doctor if your son is starting to get sick. On the day that the dose is omitted (usually just the afternoon dose as the other person indicated), I would not have him participate in heavy activities.
I have no adrenals, and I can omit the afternoon dose, and I take my pills with me, take the test and then take my pills right after the draw and I can be fine. Just the day before, I cannot tax my body heavily. HC does have a 6-8 hour half live.
If you search, you can find corticosteroid half life calculators that will show the different steroids, and their half lives, as well as if they are fast, medium or slow acting.
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