Background: Serum steroid assays play an important role in the clinical evaluation of a number of common endocrine disorders. Among various assays, tandem mass spectrometry (MS/MS) has being increasingly applied in clinical laboratories for its high sensitivity, specificity, and simultaneous multi-analyte quantitation capability. Our first generation isotope dilution steroid profile assay by HPLC-tandem MS/MS with a C-18 column allowed for the measurement of 9 steroids in 18 min employing a sample volume of 760 ul serum. We describe our second generation steroid profile assay which allows for the quantitation of 12 steroids simultaneously employing HPLC-MS/MS and isotope dilution tandem MS in 11 min. This method requires a sample volume of 200 microl.
Methods: An API-5000 triple-quadrupole mass spectrometer (Sciex, Concord, Canada) coupled with the PhotoSpray source and Shimadzu HPLC system (Shimadzu Scientific Instruments, Columbia, MD) was used employing isotope dilution with deuterium labeled internal standard (IS) for each analyte. Two hundred microliters of serum were deproteinized by adding 300 microl of acetonitrile containing internal standards. After centrifugation, 450 microl of supernatant were diluted with 900 microl of water and 1000 microl aliquot were injected onto a C-8 column. After a 3 min wash the valve was activated to initiate the gradient elution program which eluted the steroids. Quantitation by MRM analysis was performed both in positive ion mode for 11 analytes and in negative ion mode for aldosterone. Within-day and between-day precision, reliability and accuracy of this method were assessed by correlation with other MS/MS and immunoassay methods and by recovery study.
Results: Within-day CVs were <11.5% for all analytes tested and between-day CVs ranged from 3.5% to 12.2%. The results of the comparison study yield r values ranging between 0.908 and 0.999. Recovery ranged from 90% to 110%.
Conclusions: This method can simultaneously measure 12 steroids in serum within 11 min with minimal sample preparation. It can be routinely employed in a clinical environment and is attractive because of its simplicity in sample processing and high throughput.