Liquid chromatography tandem mass spectrometry assay for fast and sensitive quantification of estrone-sulfate

Background: The circulating pool of estrone-sulfate is considered as a "reservoir" of slowly-metabolized estrogen that can be exploited for assessing overall individual estrogenicity. The aim of this study was to develop a rapid and sensitive liquid chromatography-tandem mass spectrometry assay for the determination of estrone-sulfate, suitable for routine clinical investigations. Methods: The proposed assay is based on a simple protein precipitation procedure and on a fast measurement with a triple-quadrupole mass spectrometer operating in negative ion mode and in multiple reaction monitoring. The method was assessed for intra- and inter-day precision, accuracy, recovery, and clinical suitability. A comparison with available radioimmunoassay was also performed. Results: The LC-MS/MS method is able to detect estrone-sulfate concentrations ≤1 pg/mL and has a low limit of quantification of 7.8 pg/mL. Intra- and inter-day precision and accuracy were less than 10.5% and 5.0% respectively. The recovery was in the range of 93%-110%. When compared with radioimmunoassay the method resulted more accurate and therefore more suitable for quantifying the estrone-sulfate in different clinical settings, including patients treated with aromatase inhibitors. Conclusions: The proposed LC-MS/MS method represents a convincing alternative to the immunoassay for a fast, cost-effective and reliable measurement of estrone-sulfate in routine clinical investigations and in large epidemiological studies. It may contribute in shedding a new light on the diagnostic value of estrone-sulfate in normal and pathological conditions.