Dexamethasone suppression test (Cushing's)

[dyspareunia]

FA says that if ACTH is suppressed following a low-dose dexamethasone suppression test to suspect ACTH-independent cushing syndrome (adrenal tumor).

I understand the usage of the test for distinguishing other forms of Cushing's syndrome, but in a patient with an high cortisol and low ACTH, what purpose does a dexamethasone suppression test serve?

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[Transposony]

The purpose of a low dose dexamethasone suppression test is to confirm or exclude Cushing syndrome.
A normal (suppressible Pituitary) low dose dexamethasone suppression test excludes Cushing syndrome.
So, low dose dexamethasone suppression test and/or 24-hour urine cortisol are done to diagnose the presence of Cushing syndrome.
They do not tell you the cause of Cushing syndrome.

Only once you have determined that the low dose dexamethasone suppression test does not suppress the cortisol level, you do the ACTH level.
ACTH level measurement will help you to identify the cause of Cushing syndrome.

Again, you don't do the ACTH levels before doing the low dose dexamethasone suppression test.

 

[dyspareunia]

The purpose of a low dose dexamethasone suppression test is to confirm or exclude Cushing syndrome.
A normal (suppressible Pituitary) low dose dexamethasone suppression test excludes Cushing syndrome.
So, low dose dexamethasone suppression test and/or 24-hour urine cortisol are done to diagnose the presence of Cushing syndrome.
They do not tell you the cause of Cushing syndrome.

Only once you have determined that the low dose dexamethasone suppression test does not suppress the cortisol level, you do the ACTH level.
ACTH level measurement will help you to identify the cause of Cushing syndrome.

Again, you don't do the ACTH levels before doing the low dose dexamethasone suppression test.

So what is a normal result from low dose dexamethasone suppression test?

Edit: Nevermind. I just had to read the part about "you don't do ACTH levels before..." a few times before I realized what you are saying.

Thanks

 

[Burnt Almonds]

Wait, so if the low dose DXM does suppress this high cortisol level...what does that tell us? That they don't have Cushings? Even if they had high 24 hr cortisol?