ACTH result interpretation

OK, so I know that most tests, when done singly don't provide very much information, but I do have some questions regarding a stand-alone ACTH test that I just did. Namely, my result says  <5 with range as 0-46 .  

Is this how ACTH is usually measured, as a "less than" number. It just seemed odd.

Also, can I trust this lab to rule out pituitary involvement if it was taken fasting at approximately 9am and drawn into a chilled tube? I asked the tech to centrifuge it immediately, but short of seeing her do it, I have to trust that she did.

Wee bit of background, 4cm adrenal tumor discovered incidentally. Normal BP, no problem with glucose, no overt symptoms of cortisol excess. All labs for catecholamines, aldosterone, renin, DHEA, potassium, sodium etc within normal. First positives were a 24 hr UFC 164 (3 weeks post abdominal surgery)((range 10 to 80)), and serum cortisol of 4 post 11pm low dose Dex suppression (range 5-25).

I have also completed two 11pm salivary swabs, no results yet, and I've also done another dex suppression, this time it was .5mg every 6 hours for 48hrs followed by 24 hr urine catch, no results yet.

I am beginning to think the ACTH test is useless unless it was taken with a serum cortisol. However, I'd like to think, that even without cortisol, or even if cortisol is high, IF the feedback loop was working properly, I would have a low ACTH regardless. ACTH would only be high if a pit tumor was secreting independently, right (?).

thanks for any input

[rumpled]

It looks like lousy lab handling to me. Even if she *did* centrifuge it, which may or may not have happened, it may not have been frozen right away...

I would ask for a re-do and get another lab tech or lab to do it.

[upbeat63333]

What would be your suspicion that it wasn't done right--besides the fact that labs and techs don't often do it right?

When I handed in the request, I had written "chilled tube, centrifuge immediately, ICE (in caps)".

She did draw into a chilled tube for sure, while she was drawing I did ask that she centrifuge immediately, and she said she would.

I didn't follow her to the back of the lab to ensure she did that, nor did I see her freeze it, but short of purposeful negligence, I have to assume she did it correctly. It was written and verbally requested! I don't think any of us could trust any result of ACTH in that case.

Can you please advise if you think the result of my ACTH test is one that I should expect to see in the context of all other results so far? Or can you give me your thoughts on why you think it is off from what I would expect to see?.

Also, I'm a little confused on this point, in everything I've read, it says ACTH should be at its *highest* near 8am. But if its in a negative feedback loop with cortisol, shouldn't ACTH be *nearing it's lowest* at 8am when cortisol is nearing its highest? Higher cortisol would have the effect of lowering ACTH wouldn't it?