Stable-isotope dilution LC–ESI-MS/MS techniques for the quantification of total homocysteine in human plasma

Homocysteine is an endogenous sulphydryl aminoacid irreversibly catabolized by transsulfuration to cysteine or remethylated to methionine. Increased plasma levels of homocysteine are an independent risk factor for atherosclerosis and cardiovascular disease. Accurate and reliable quantification of this amino acid in plasma samples is essential in clinical practice to explore the presence of a hyperhomocysteinemia, for instance after an ischemic event, or to control a possible adjunctive risk factor in patients at higher risk. In this review, LC–ESI-MS/MS methods are discussed and compared with other analytical methods for plasma homocysteine. LC–ESI-MS/MS is a technique combining the physicochemical separation of liquid chromatography with the analysis of mass spectrometry. It is based on stable-isotope dilution and possesses inherent accuracy and precision. Quantitative analysis is achieved by using commercially available homocystine-d8 as an internal standard. Taking advantage of the high sensitivity and specificity, approaches involving LC–ESI-MS/MS require less laborious sample preparation, no derivatization and produce reliable results.