Annals of Clinical Biochemistry > Volume 45, Number 4 > Pp. 380-388

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Wood, L. Articles by Turkes, A. Search for Related Content PubMed PubMed Citation Social Bookmarking                      What's this?

Original Articles

Measurement of urinary free cortisol by tandem mass spectrometry and comparison with results obtained by gas chromatography-mass spectrometry and two commercial immunoassays

Lisa Wood¹, David H Ducroq², Helen L Fraser², Scott Gillingwater³, Carol Evans¹, Alan J Pickett¹, Derek W Rees¹, Rhys John¹ and Atilla Turkes¹

¹ Department of Medical Biochemistry and Immunology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, UK; ² WEQAS, Reference Laboratory, The Quadrant Centre, Cardiff Business Park, Llanishen, Cardiff CF14 5WF, UK; ³ Waters Corporation, MS Technologies Centre, Atlas Park, Simonsway, Manchester M22 5PP, UK

Corresponding author: Dr A Turkes. Email: atilla.turkes{at}cardiffandvale.wales.nhs.uk

Background: Determination of urinary free cortisol (UFC) is an important adjunct for the assessment of adrenal function. In this study, we have analysed cortisol concentrations in urine samples by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-tandem mass spectrometry (LC-MS/MS) and two immunoassays. The results were compared with GC-MS. The interference of cortisol ring-A metabolites in immunoassays was also assessed.

Methods: The GC-MS technique involved solvent extraction, LH-20 clean-up and derivatization. Only solid-phase extraction procedure was used for LC-MS/MS. The samples were analysed in positive electro-spray ionization mode, monitoring the transitions for cortisol and deuterated-cortisol at m/z 363.3 > 121.2 and m/z 365.3 > 122.2, respectively. Immunoassays were performed according to the manufacturer's instructions.

Results: When compared with GC-MS results both immunoassays (Coat-A-Count; approximately 1.9-fold, Centaur; approximately 1.6-fold) overestimated UFC concentrations. Cortisol ring-A dihydro- and tetrahydrometabolites contribute significantly to this overestimation. There was no interference by these metabolites in either GC-MS or LC-MS/MS methods. The sensitivity of the LC-MS/MS procedure was 2 nmol/L and the intra- and inter-assay variations were <5% in each quality-control sample. The comparison of the UFC results achieved by assaying the study samples with GC-MS and LC-MS/MS indicated that the agreement between the two methods was excellent (LC-MS/MS = 1.0036GC-MS – 0.0841; r² = 0.9937).

Conclusions: The interference of cortisol ring-A metabolites in immunoassays contribute to overestimation of UFC concentrations. The LC-MS/MS procedure had the sensitivity, specificity, linearity, precision and accuracy for the determination of UFC concentrations. The method is suitable for routine use provided that method-dependant reference values are established.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?