PAPER-CHROMATOGRAPHY PRIOR TO CORTISOL RIA ALLOWS FOR ACCURATE USE OFTHE DEXAMETHASONE SUPPRESSION TEST IN CHRONIC-RENAL-FAILURE

The assessment of the hypothalamic-pituitary-adrenal axis in patients with chronic renal failure (CRF) on hemodialysis is often hampered by abnormal responses to the standard 1-mg dexamethasone suppression test , Various mechanisms have been preposed to explain this lack of suppre ssibility, The present study was designed to look into the mechanisms possible for these findings in patients with CRF. We studied 6 patient s with CRF on hemodialysis and 5 healthy subjects utilizing the 1-mg d examethasone suppression test as well as the 50-mg hydrocortisone supp ression test. Samples were assayed for dexamethasone, adrenocorticotro pic hormone, corticosterone, and cortisol by both direct radioimmunoas say (RIA) and RIA after paper chromatography, Utilizing the direct cor tisol RIA, 4 of 6 patients with CRF exhibited blunted dexamethasone su ppression, while all 6 patients showed normal suppressibility after de xamethasone when cortisol was measured after paper chromatography. In contrast, all controls showed normal suppressibility regardless of the cortisol assay procedure used. The hydrocortisone suppression test wa s unreliable in the setting of CRF. Mean dexamethasone levels were sim ilar in both groups, Plasma adrenocorticotropic hormone levels were si gnificantly higher in the CRF patients, possibly indicative of an unde rlying hypothalamic-pituitary-adrenal axis abnormality. Abnormalities in dexamethasone suppression testing in patients with CRI; may be expl ained by the overestimation of cortisol levels by direct RIA rather th an by alteration of dexamethasone absorption or metabolism. Measuremen t of cortisol after paper chromatography is superior to direct RTA of cortisol. in patients with CRF.