Cortisol and cortisone analysis in serum and plasma by atmospheric pressure photoionization tandem mass spectrometry

Objectives: Cortisol metabolism is controlled by 11beta-hydroxysteroid dehydrogenase (11beta-HSD) isoenzymes, which interconvert cortisol and cortisone. Accurate measurement of the cortisol and cortisone concentrations and their ratio provide useful information about 11beta-HSD activity. Methods: Cortisol and cortisone were extracted with methyl-tert-butyl ether from 100 mul of serum or plasma. The extract was evaporated, reconstituted with mobile phase, and analyzed by tandem mass spectrometry using a photoionization interface. The transitions monitored were: m/z 363 to 121 and 363 to 97 for cortisol, 361 to 163 and 361 to 105 for cortisone. Results: Within-run and between-run coefficients of variation were less than 6% and 12%; 14% and 22%; 11% and 21% for cortisol, cortisone, and their ratio, respectively. The limit of detection was 1 mug/l for cortisol and 5 mug/l for cortisone. Normal ranges for cortisol and cortisone concentration and for their ratio in plasma (n = 120) determined as the central 95% were 33-246 mug/l for cortisol, 8-27 mug/l for cortisone, and 0.081-0.301 for the cortisone/cortisol ratio. Conclusions: We developed a simple sensitive method for cortisol and cortisone analysis in plasma and serum that uses a small sample volume. The method is very specific, fast, does not have any known interference, and is useful for diagnosis of variety of disease and pathologic conditions. (C) 2004 The Canadian Society of Clinical Chemists. All rights reserved.