Urine free cortisol analysis by automated immunoassay and high-performance liquid chromatography for the investigation of Cushing's syndrome.
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.
Ching
Simon Y L
SY
Clinical Biochemistry Department, PathWest Laboratory Medicine, Queen Elizabeth II Medical Centre, Nedlands, Western Australia.
Lim
Ee Mun
EM
Beilby
John
J
Bhagat
Chotoo
C
Rossi
Enrico
E
Walsh
John P
JP
Pullan
Peter
P
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
D006854:Hydrocortisone