Dried blood spots analysis of 6β‐hydroxycortisol and cortisol using liquid chromatography/tandem mass spectrometry for calculating 6β‐hydroxycortisol to cortisol ratio

Abstract

AbstractDried blood spot (DBS) sampling is a minimally invasive method used to collect blood samples of any population for personalized medicine. We aimed to develop a sensitive and reliable analytical method for measuring 6β‐hydroxycortisol (6β‐OHF) and cortisol concentrations in DBS by liquid chromatography/tandem mass spectrometry so as to utilize DBS as a less invasive blood sampling method for calculating the ratio of 6β‐OHF/cortisol. The lower limits of quantification obtained using four DBS were 1.08 pg/50 μl for 6β‐OHF and 1.01 pg/50 μl for cortisol. The 6β‐OHF and cortisol in DBS were stable for 28 days at room temperature. The intraday and interday accuracy and precision of the method was <12%. Additionally, the 6β‐OHF and cortisol in DBS were measured before, during, and after 3 days of clarithromycin administration to two of the subjects. Then, their concentration was compared in the plasma and whole blood collected simultaneously. The concentrations of 6β‐OHF and cortisol in four DBS ranged from 0.007 to 0.079 ng/50 μl and from 1.15 to 6.66 ng/50 μl, respectively. The 6β‐OHF/cortisol ratio in DBS decreased by approximately 50% on administering clarithromycin compared with that before the administration of clarithromycin. The 6β‐OHF/cortisol ratio in DBS also showed a strong correlation with that in whole blood (r = 0.9694) and plasma (r = 0.9383). This method provides high accuracy and precision for measuring 6β‐OHF and cortisol in DBS. It also allows the use of DBS instead of plasma for calculating the 6β‐OHF/cortisol ratio. The 6β‐OHF/cortisol ratio could be an index of CYP3A activity in clinical setting.