Monitoring dexamethasone suppression test by simultaneous LC-MS/MS measurement of cortisol, cortisone and dexamethasone in serum samples

Background: the simultaneous monitoring of dexamethasone and cortisol serum concentrations by LC-MS/MS has recently proven to effectively increase the diagnostic performance of overnight dexamethasone suppression in comparison to cortisol immunometric measurement performed in the majority of clinical biochemistry laboratories. Methods: an in-house LC-MS/MS method for the quantification of cortisol, cortisone and dexamethasone in serum/plasma matrix was employed for the analysis of 297 serum samples collected from patients with suspected hypercortisolism subjected to dexamethasone suppression tests at three different dosages. Cortisol concentrations obtained by LC-MS/MS analysis were also compared with the one resulted from routine chemiluminescent immunoassay (CLIA) measurements. Results: dexamethasone concentrations were significantly different in patients performing the low-dose dexamethasone suppression test (LDDST) and dexamethasone suppression test (DST) and higher than the proposed cut-off for accepting dexamethasone suppression test results for all tested patients. LC-MS/MS showed a negative bias of 6.8% when compared to CLIA method, with relevant differences at low concentrations. Cortisol and cortisone showed similar concentration patterns in patient categorized as positive or negative to LLDST and DST by cortisol immunometric measurement. Conclusions: the present study proved the overall performance of previously developed LC-MS/MS method for the measurement of cortisol, cortisone and dexamethasone in real clinical serum samples, guaranteeing a single and versatile analytical tool to be implemented in clinical biochemistry laboratory’s routine. The obtained results showed that the administered dexamethasone dosage was sufficient to reach test acceptance threshold in all monitored patients; the correlation between cortisol and cortisone serum concentrations could open the way to the future addition of cortisone measurement to the monitoring dexamethasone suppression test results.