title: Urine free cortisol analysis by automated immunoassay and high-performance liquid chromatography for the investigation of Cushing's syndrome.
abstract: BACKGROUND
  We compared a widely used immunoassay method for urine free corticoids with a high-performance liquid chromatography (HPLC) method for the investigation of Cushing's syndrome.
  
  
  METHODS
  Urine free corticoid analysis using an Immulite:2000 automated immunoassay analyser and urine free cortisol analysis by a specific HPLC method on 39 patients with an elevated baseline immunoassay 24 h urine free corticoid result who were referred from 2000 to 2004.
  
  
  RESULTS
  Reference ranges for urine free corticoids by immunoassay and for urine free cortisol by HPLC were <900 and <170 nmol/day, respectively. Of the 39 patients with an elevated immunoassay urine free corticoid result, Cushing's syndrome was surgically proven in 22 patients, giving a positive predictive value of 56%. Cushing's syndrome was excluded in 12 of the remaining 17 patients by applying the specific HPLC method and at least one of the following: a clinical evaluation which was not suggestive or adequate suppression of plasma cortisol following dexamethasone. Urine free cortisol analysis by HPLC gave a positive predictive value of 81% for Cushing's syndrome.
  
  
  CONCLUSIONS
  Although immunoassay has a low specificity for urine cortisol, it is a widely available test which serves as a valid initial investigation of Cushing's syndrome.
authors.affiliation: Clinical Biochemistry Department, PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre, Nedlands, Western Australia.
authors.forename: Simon Y L
authors.initials: SY
authors.lastname: Ching
authors.forename: Ee Mun
authors.initials: EM
authors.lastname: Lim
authors.forename: John
authors.initials: J
authors.lastname: Beilby
authors.forename: Chotoo
authors.initials: C
authors.lastname: Bhagat
authors.forename: Enrico
authors.initials: E
authors.lastname: Rossi
authors.forename: John P
authors.initials: JP
authors.lastname: Walsh
authors.forename: Peter
authors.initials: P
authors.lastname: Pullan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003480:Cushing Syndrome / Q000175:diagnosis* / Q000652:urine; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism / Q000652:urine*; D007118:Immunoassay / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D006854:Hydrocortisone