Distinguish the appropriate test to diagnose pituitary-adrenal axis dysfunction.

Explanation:

To see if the pituitary is doing its job of secreting ACTH-We can stop steroid production in the adrenals by blocking one of the converting enzymes and seeing if ACTH increases to make up for the inhibition. The compound used to do this job is Metyrapone. The conversion of serum 11 deoxycortisol (11DOC )(which is excreted in urine as 17 hydroxycorticosterone (17HOCS) is blocked from becoming cortisol therefore these precursors will rise if the block is effective and the adrenal is functional AND the pituitary is responding correctly. There will be a hyper-response in Cushings disease.

ACTH and steroid producing tumors are not affected by metyrapone

What used to confuse me in the past is as follows-

One could give CRH(Corticotropin Releasing Hormone stimulation test) and check level of ACTH which in the normal person will go up but will not if pituitary is destroyed. Therefore this tests the pituitary but not the axis.

To see if the adrenal is doing its job by responding to ACTH - give exogenous ACTH(ACTH stim test) and check the level of cortisol which in the normal person will go up but in Addison's disease will not rise. These are of 2 types-short and long. Short is completed in 1/2 to 1 hour and whosoever turns out to be underactive gets the long test. Therefore this tests the adrenal but not the axis.