title: A comparison of the overnight and the standard metyrapone test for the differential diagnosis of adrenocorticotrophin-dependent Cushing's syndrome.
abstract: OBJECTIVE
  We wished to develop optimal criteria for interpreting the single-dose overnight metyrapone test and to compare the diagnostic efficiency of the overnight and the standard 6-dose metyrapone tests for the differential diagnosis of ACTH-dependent Cushing's syndrome.
  
  
  METHODS
  Retrospective pilot study based on all patients who completed both metyrapone tests and whose diagnoses were subsequently confirmed surgically.
  
  
  METHODS
  Sixty-three patients, 57 with pituitary tumours and 6 with ectopic ACTH syndrome, were studied.
  
  
  METHODS
  The sensitivity and specificity were determined using stimulation of plasma 11-deoxycortisol and suppression of plasma cortisol as endpoints for the overnight test and stimulation of urine 17-hydroxysteroid and plasma 11-deoxycortisol as endpoints for the standard test. The lest response that gave the highest sensitivity for the diagnosis of Cushing's disease, with 100% specificity, was determined for each test endpoint.
  
  
  RESULTS
  Both the stimulation of plasma 11-deoxycortisol and the suppression of plasma cortisol were expressed as the ratio of the post-metyrapone value to baseline. A plasma 11-deoxycortisol ratio > than 220 or a plasma cortisol ratio > 0.6 was associated with 100% specificity for diagnosis of Cushing's disease by the overnight test. When these two criteria were combined, the sensitivity was 65%, which was significantly higher than that obtained using either steroid alone: 42% for both plasma 11-deoxycortisol and plasma cortisol. The sensitivity of 65% for the overnight test, at 100% specificity, was nearly identical to that of the standard test in the same patients: 67% for the combined criterion of > 70% stimulation of urine 17-hydroxysteroid or > 480-fold increase of plasma 11-deoxycortisol. When the criteria for both the overnight and standard tests were combined, the sensitivity increased to 84%, which was higher than that obtained using the criteria for either test alone (P < 0.02).
  
  
  CONCLUSIONS
  The single-dose overnight metyrapone test, which can be performed in 24 hours and which avoids the disadvantages associated with timed urine collections, has a nearly identical sensitivity (for a specificity of 100%) as the 6-dose standard metyrapone test for the diagnosis of Cushing's disease. Furthermore, the diagnostic performance of a criterion that combines the results of both tests is significantly better than the best criterion for either test alone.
authors.affiliation: Developmental Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: P C
authors.initials: PC
authors.lastname: Avgerinos
authors.forename: L K
authors.initials: LK
authors.lastname: Nieman
authors.forename: E H
authors.initials: EH
authors.lastname: Oldfield
authors.forename: G B
authors.initials: GB
authors.lastname: Cutler
mesh_terms: D000182:ACTH Syndrome, Ectopic / Q000097:blood / Q000150:complications; D003350:Cortodoxone / Q000097:blood; D003480:Cushing Syndrome / Q000097:blood / Q000175:diagnosis* / Q000209:etiology; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008797:Metyrapone; D010865:Pilot Projects; D010911:Pituitary Neoplasms / Q000097:blood / Q000150:complications; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
chemical_list: D003350:Cortodoxone; D006854:Hydrocortisone; D008797:Metyrapone