title: Cortisol production rates in subjects with suspected Cushing's syndrome: assessment by stable isotope dilution methodology and comparison to other diagnostic methods.
abstract: It can be difficult to establish the diagnosis of Cushing's Syndrome (CS) in patients with mild or nonspecific clinical and biochemical findings, because available diagnostic tests have limited predictive values. We hypothesized that measurement of 24-h cortisol production rates (CPRs) might be a more sensitive indicator of CS in such patients. We measured CPRs in 28 patients with suspected CS (but equivocal biochemical findings) and in 22 healthy control subjects, by infusing tracer amounts of deuterated cortisol, with simultaneous measurements of 24-h urine free cortisol (UFC) levels; and we frequently sampled serum cortisol levels. CPRs were calculated from the ratio of isotopic enrichment to isotopic dilution of cortisol measured by gas chromatography-negative ion chemical ionization mass spectrometry. Nine of the patients proved to have CS by surgery (CS-Yes), whereas 19 patients were determined not to have CS by biochemical testing (CS-No). Mean 24-h UFCs, nocturnal serum cortisol levels, and CPRs were higher in CS-Yes, compared with CS-No and normal subjects. However, one CS-Yes patient had a normal 24-h UFC, two had normal nocturnal serum cortisol levels, and two had normal 24-h CPRs. There was extensive overlap in all of the biochemical parameters between the CS-Yes and the CS-No groups. Thus, measurement of CPR does not seem to offer any diagnostic advantage over available tests for the diagnosis of CS. Patients with proven CS can have normal UFC levels, normal CPRs, or normal nocturnal cortisol levels, whereas patients not thought to have CS may have elevated levels of any one or more these parameters.
authors.affiliation: Division of Endocrinology, Diabetes, and Clinical Nutrition, Oregon Health Sciences University, Portland 97201, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Samuels
authors.forename: D D
authors.initials: DD
authors.lastname: Brandon
authors.forename: L M
authors.initials: LM
authors.lastname: Isabelle
authors.forename: D M
authors.initials: DM
authors.lastname: Cook
authors.forename: K E
authors.initials: KE
authors.lastname: Graham
authors.forename: J Q
authors.initials: JQ
authors.lastname: Purnell
authors.forename: D L
authors.initials: DL
authors.lastname: Loriaux
mesh_terms: D000328:Adult; D000368:Aged; D002849:Chromatography, Gas; D002940:Circadian Rhythm / Q000502:physiology; D003480:Cushing Syndrome / Q000097:blood* / Q000175:diagnosis*; D003903:Deuterium; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood* / Q000652:urine; D008297:Male; D008875:Middle Aged; D011865:Radioisotope Dilution Technique; D012044:Regression Analysis; D013057:Spectrum Analysis
chemical_list: D003903:Deuterium; D006854:Hydrocortisone