title: Assessment of endogenous, oral and inhaled steroid cross-reactivity in the Roche cortisol immunoassay.
abstract: BACKGROUND
  Inhaled steroids are widely used for the treatment of asthma. Concerns over adrenal suppression when used at high doses or in combination with drugs such as ritonavir exist, requiring the measurement of serum cortisol. Herein, we investigate the cross-reactivity of the inhaled steroids betamethasone, fluticasone and beclomethasone in the Roche cortisol immunoassay, in addition to five other steroids.
  
  
  METHODS
  Five replicates were produced from a serum pool for each of the eight steroids at a final concentration of 0.1 and 1 µg/mL. Each steroid was dissolved in 50% methanol, with 50% methanol of the same volume added to the control sample. The cross-reactivity of each steroid in the cortisol assay was calculated.
  
  
  RESULTS
  There was no statistically or clinically significant cross-reactivity in the measurement of cortisol when fluticasone, beclomethasone or betamethasone were spiked at 0.1 and 1.0 µg/mL, except for beclomethasone at a concentration of 1 µg/mL (1490 nmol/L) with a cross-reactivity of 1.6%, which is unlikely to be clinically significant. At both steroid concentrations investigated, prednisolone, 17-hydroxyprogesterone and 11-deoxycortisol exhibited statistically significant cross-reactivities that were greater than the least significant change of the assay (13.1%), whereas dexamethasone and metyrapone did not. Mean inter-assay precision was 1.5% (405-1586 nmol/L).
  
  
  CONCLUSIONS
  The cross-reactivity of the inhaled steroids; betamethasone, fluticasone and beclomethasone in the Roche cortisol immunoassay are unlikely to be clinically significant at the concentrations found in patients on therapeutic doses. This will enable confident assessment of adrenal status in patients at risk of adrenal suppression.
authors.affiliation: Department of Clinical Biochemistry and Metabolic Medicine, Royal Liverpool and Broadgreen University Hospitals Trust, Liverpool, UK felicity.stokes@rlbuht.nhs.uk.
authors.forename: F J
authors.initials: FJ
authors.lastname: Stokes
authors.affiliation: Department of Clinical Biochemistry and Metabolic Medicine, Royal Liverpool and Broadgreen University Hospitals Trust, Liverpool, UK.
authors.forename: L M
authors.initials: LM
authors.lastname: Bailey
authors.affiliation: Department of Molecular and Clinical Pharmacology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK.
authors.forename: A
authors.initials: A
authors.lastname: Ganguli
authors.affiliation: Department of Clinical Biochemistry and Metabolic Medicine, Royal Liverpool and Broadgreen University Hospitals Trust, Liverpool, UK.
authors.forename: A S
authors.initials: AS
authors.lastname: Davison
mesh_terms: D000280:Administration, Inhalation; D000284:Administration, Oral; D000730:Androstadienes / Q000008:administration & dosage / Q000493:pharmacokinetics*; D018927:Anti-Asthmatic Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D001507:Beclomethasone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D001623:Betamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D003429:Cross Reactions; D065692:Cytochrome P-450 CYP3A Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics; D005260:Female; D000068298:Fluticasone; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods; D008297:Male; D019438:Ritonavir / Q000008:administration & dosage / Q000493:pharmacokinetics
chemical_list: D000730:Androstadienes; D018927:Anti-Asthmatic Agents; D065692:Cytochrome P-450 CYP3A Inhibitors; D001623:Betamethasone; D000068298:Fluticasone; D001507:Beclomethasone; D019438:Ritonavir; D006854:Hydrocortisone
keywords: Cortisol; cross-reactivity; immunoassay; inhaled steroids; steroids