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Horm Metab Res 2011; 43(10): 714-719
DOI: 10.1055/s-0031-1286297
Humans, Clinical
Georg Thieme Verlag KG Stuttgart · New York

Measurement of Urinary Free Cortisol by Current Immunoassays: Need for Sex-dependent Reference Ranges to Define Hypercortisolism

T. Deutschbein
1   Department of Endocrinology and Division of Laboratory Research, University of Duisburg-Essen, Essen, Germany
,
M. Broecker-Preuss
1   Department of Endocrinology and Division of Laboratory Research, University of Duisburg-Essen, Essen, Germany
,
M. F. Hartmann
2   Steroid Research & Mass Spectrometry Unit, Center of Child and Adolescent Medicine, Justus Liebig University, Giessen, Germany
,
R. Althoff
1   Department of Endocrinology and Division of Laboratory Research, University of Duisburg-Essen, Essen, Germany
,
S. A. Wudy
2   Steroid Research & Mass Spectrometry Unit, Center of Child and Adolescent Medicine, Justus Liebig University, Giessen, Germany
,
K. Mann
1   Department of Endocrinology and Division of Laboratory Research, University of Duisburg-Essen, Essen, Germany
,
S. Petersenn
1   Department of Endocrinology and Division of Laboratory Research, University of Duisburg-Essen, Essen, Germany
› Author Affiliations
Further Information

Publication History

received 19 December 2010

accepted after secondrevision 11 August 2011

Publication Date:
19 September 2011 (online)

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Abstract

Urinary free cortisol (UFC) is used to assess disease activity in hypercortisolemic patients. However, reference ranges are often lacking, especially with respect to potential confounding variables. This study analyzed upper limits of normal (ULN, mean + 2 SD) for 2 newer immunoassays, using gas chromatography-mass spectrometry (GC-MS) as reference method. Each 10 healthy subjects were grouped by age (18–29; 30–49; ≥ 50 years), BMI (< 25; ≥ 25 kg/m2), and sex, resulting in a total of 120 controls (60 males; age: 39.3±1.3 years; BMI: 25.9±0.4 kg/m2). ULN were calculated for a radioimmunoassay (RIA, Immunotech) and an electrochemiluminescence immunoassay (ECLIA, Roche) and applied to 12 hypercortisolemic patients (4 males; age: 53.1±3.1 years; BMI: 29.1±1.8 kg/m2). To determine degradation, samples were stored at 4°C (without light) or 22°C (with and without light) for 0, 24, and 72 h. Cortisol concentrations were significantly correlated: r=0.88 for RIA vs. ECLIA, r=0.75 for RIA vs. GC-MS, and r=0.77 for ECLIA vs. GC-MS (always p<0.0001). For each procedure, multiple stepwise regression analysis identified sex as the only significant predictor, resulting in sex-dependent ULN (males vs. females): 294 vs. 208 nmol/24 h (RIA), and 379 vs. 277 nmol/24 h (ECLIA). These ULN classified samples from patients as hypercortisolemic in 100% (RIA) and 95% (ECLIA). Different storage conditions over 72 h did not alter UFC levels significantly. Results of the 3 procedures were well correlated, and the use of assay- and sex-specific ULN allowed excellent identification of hypercortisolic states. UFC is stable over 72 h irrespective of the storage conditions applied.

Key words

age - body mass index (BMI) - cortisol - gender - reference range - urinary free cortisol (UFC) - storage
 

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