Dex suppression .6?

Had a cortisol dexamethasone supp. test and want to know what this means:  .6L ug/dL with a range of 2.3-19.4 (am range 6.2-19.4).   Overnight test. Was I supposed to be suppressed?  That's normal or not?  I'm reposting this from the autoimmune forum. If it means I'm not adrenal cushings, could it still be pituitary?  Or just a missed high on cyclical?  Why is it so low?

[rumpled]

The dex test is not a perfect one for patients - but an inexperienced doctor will see it as a test of exclusion. An expert will see it more as a test of location.

You *failed* the test for most - in that you suppressed. The range given is not for the test, it is for the normal test. The lab does not print the range for suppression. In the US the cut off is 1.8.

I had the cyclical form of Cushing's myself and failed all the dex suppression tests. I still had Cushing's - pituitary source. Pituitary source is more common than adrenal.

This is how the test is interpreted:
"Cushing syndrome caused by an adrenal tumor:

    Low-dose test: no change
    ACTH level: low
    In most cases, the high-dose test is not needed

Cushing syndrome related to an ectopic ACTH-producing tumor:

    Low-dose test: no change
    ACTH level: high
    High-dose test: no change

Cushing syndrome caused by a pituitary tumor (Cushing's disease)

    Low-dose test: no change
    High-dose test: normal suppression (however, some do not suppress, and another test is needed)"

However, if you take into consideration how ACTH and dex work together and if the doctor thought about that... dex suppresses ACTH down (I use it to keep my near 4000 down to 400) and that in turn would make the cortisol receptors in the adrenals not be activated. If the tumor was in the adrenal, then the level would be high (it would not need the ACTH to give off cortisol), and to be low just means the dex is working like it should. So a low test just has to be taken as part of the puzzle - just one of the tests - not just a single test on its own. Sadly I know a LOT of docs that run just that test and tell people that they are ok!

It is low due to the dex... my best guess.

[Squishyleo]

That makes the most sense to me so far!  Thank you so much. What test played the biggest part in your diagnosis, if you don't mind me asking?

[rumpled]

There is no *one* test - so the doctor should look at a bunch to make a diagnosis.

I know quite a few people with the disease and some of us do better, oddly, with one test or another. I failed all stim tests (still do!!!) and did ok on free cortisol tests like saliva and urine, but not the 24 hour as I was so low during the day and so low at night, my average was normal. What spotlighted this was a 10 hour urine that only took the night time urine - and I was super high but few doctors know or accept this test. That test I only took my second round - post pituitary surgery seeing if surgery failed and if I needed another surgery. I did. Some do well with midnight blood draws, late night salivas, or 8 am serums - so you have to know from testing what works and the doc has to let you test.