Analysis of cortisol, cortisone and dexamethasone in human serum using liquid chromatography tandem mass spectrometry and assessment of cortisol: Cortisone ratios in patients with impaired kidney function

We developed a high sensitivity method for simultaneous measurement of cortisol, cortisone and dexamethasone. Using this method, we compared concentrations of cortisol, cortisone and their ratios in samples from intensive care unit (ICU) and non-ICU patients, and cortisol and dexamethasone concentrations in patients with Cushing's and suspected Cushing's syndrome. Two hundred microliters of human serum aliquots were extracted using solid phase extraction and analyzed using liquid chromatography–tandem mass spectrometry. Primary mass transitions monitored for cortisol, cortisone and dexamethasone were m/z 363/121, 361/163 and 393/373 respectively. The limits of quantification for cortisol and cortisone were 0.3 μg/l (0.8 nmol/l) and for dexamethasone it was 0.5 μg/l (1.2 nmol/l). Total imprecision was < 10.9%. Median cortisol to cortisone ratio of ICU patient samples was found to be 2 times higher than non-ICU samples. 54.2% of patients after 1 mg dose of overnight dexamethasone could be categorized as consistent with Cushing's syndrome. The method has high sensitivity and specificity. High cortisol to cortisone ratios in samples from ICU patients suggest change in activity of 11β-hydroxysteroid dehydrogenase in modulation of systemically available cortisol. Simultaneous measurement of dexamethasone and cortisol can be used to differentially diagnose diseases causing increased concentrations of cortisol.