Objectives: Measurement of 24-h cortisol production rate (CPR) using steady-state infusion of deuterated cortisol and analysis of stable-isotope dilution by MS is a valuable tool to examine hypothalamic-pituitary-adrenal axis activity in humans. We have developed and validated an improved method for measuring cortisol dilution with contemporary LC-MS technology. Design and methods: Plasma samples and calibrators were extracted with ethylacetate. LC-MS was performed with a Surveyor HPLC and TSQ Quantum triple-quadrupole mass spectrometer equipped with an atmospheric pressure chemical ionization (APCI) source. Results: Selectivity was improved over previous methods via elimination of an interferent identified as 20β-dihydrocortisol. The LLOQ for cortisol-d3 was 2.73nmol/L and LOD 1.37nmol/L. Plasma calibrators were linear over the concentration range 1.5-10% cortisol-d3, with correlation coefficients >0.995. Conclusions: This APCI LC-MS method offers simplified sample work-up and analysis and enables selective detection of the low concentration of cortisol-d3 infused for determination of 24-h CPR.
- Atmospheric pressure chemical ionization
- Cortisol production rate
- Liquid chromatography-mass spectrometry
ASJC Scopus subject areas
- Clinical Biochemistry