title: Dexamethasone suppression test: development of a method for simultaneous determination of cortisol and dexamethasone in human plasma by liquid chromatography/tandem mass spectrometry.
abstract: BACKGROUND
  Dexamethasone is a synthetic glucocorticoid and is analogous to cortisol. It is used in the low-dose overnight dexamethasone suppression test (LDODST) to diagnose hypercortisolism in patients suspected to be suffering from Cushing's syndrome (CS). Measuring plasma dexamethasone in conjunction with measuring the amount of cortisol following the LDODST may allow clinicians to improve the diagnosis of CS.
  
  
  METHODS
  Plasma samples were cleaned up by solid-phase extraction before analysis. Liquid chromatographic separation was carried out under reversed-phase conditions prior to detection by tandem mass spectrometry. The analytes were determined in the presence of deuterated internal standards cortisol-d4 and dexamethasone-d4.
  
  
  RESULTS
  Limit of quantitation (LOQ) was 1.89 nmol/L for dexamethasone and <0.02 μmol/L for cortisol. Recoveries of both analytes ranged from 80.2% to 114.4%. Intra- and interassay coefficients of variation were <15%. The concentration of dexamethasone and cortisol was determined in 62 patients after performing LDODST. Dexamethasone concentrations ranged from 3.0 to 21.5 nmol/L (median 7.4 nmol/L) for 57 of these samples. For five patients the concentration was <LOQ. Cortisol concentrations were <0.08 μmol/L (median 0.037 μmol/L, n = 54) except for eight patients (>0.22 μmol/L).
  
  
  CONCLUSIONS
  A method for the simultaneous measurement of dexamethasone and cortisol in human plasma by liquid chromatography/tandem mass spectrometry has been developed and validated. The method is suitable for controlling the compliance to the LDODST and for determining the cortisol plasma concentration after the test. The interpretation of LDODSTs was improved by the simultaneous determination of both analytes.
authors.affiliation: Medisch Spectrum Twente Laboratory, PO Box 50000, 7500 KA, Enschede, The Netherlands. c.hempen@mst.nl
authors.forename: C
authors.initials: C
authors.lastname: Hempen
authors.forename: S
authors.initials: S
authors.lastname: Elfering
authors.forename: A H L
authors.initials: AH
authors.lastname: Mulder
authors.forename: F A J T M
authors.initials: FA
authors.lastname: van den Bergh
authors.forename: R G H J
authors.initials: RG
authors.lastname: Maatman
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D003907:Dexamethasone / Q000097:blood*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D057230:Limit of Detection; D012015:Reference Standards; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D003907:Dexamethasone; D006854:Hydrocortisone