Hypothalamic-pituitary-adrenal axis function after inhaled corticosteroids: Unreliability of urinary free cortisol estimation

Free cortisol in the urine (UFC) is frequently measured in clinical research to assess whether inhaled corticosteroids (ICS) cause suppression of the hypothalamic-pituitary-adrenal axis. Thirteen healthy male subjects received single inhaled doses (of molar equivalence) of fluticasone propionate (FP), triamcinolone acetonide (TAA), budesonide (BUD), and placebo in this single blind, randomized, cross-over study. UFC output was measured using four commercial immunoassays in samples collected in 12-h aliquots over 24 h. The cortisol production rate was assessed from the outputs of cortisol metabolites. UFC showed a 100% increase over placebo levels in the Abbott TDX assay after the administration of BUD. The other assays detected variable suppression (ranging from 29-61% suppression for FP, 30-62% suppression for TAA, and 25% suppression to 100% stimulation for BUD). Suppression was more pronounced in the first 12 h after TAA and in the second 12 h after FP. Similar suppression was found in each 12-h period after BUD. UFC estimation based on immunoassays after ICS may be an unreliable surrogate marker of adrenal suppression. Many of the published studies describing or comparing the safety of different ICS should be reevaluated, and some should be interpreted with caution.