Performance comparison of three assay methods used in fasting and postmethionine load plasma homocysteine determinations from patients with vascular disease

Several methods have been developed for measurement of plasma total homocysteine (tHcy), a proven graded risk factor for cardiovascular diseases. The aim of the study was to compare 3 commonly used clinical methods (enzyme immunoassay, Axis Biochemicals, Oslo, Norway; and fluorescence polarization immunoassay [FPIA], Axis, on the Abbott IMx System, Abbott Laboratories, Abbott Park, IL; and BioRad high-performance liquid chromatography [HPLC], Laboratories, Munich, Germany) for tHcy determination in samples from cardiovascular patients also undergoing methionine load measurement. Only HPLC reached the required coefficient of variation (<6%) for desirable performance for tHcy concentrations ranging between 0.68 and 5.41 mg/L (5 and 40 micromol/L). A higher variability was observed for postmethionine load vs fasting samples, which reached statistical significance for FPIA (P = .0013). The closest agreement between methods was observed between HPLC and FPIA for fasting tHcy concentrations (-0.23 mg/L [-1.69 micromol/L], -30% to 8%).Both immunoassays could be suitable alternatives for laboratories with high workloads when HPLC is not available. Differences among tHcy values must be taken into account when these methods will be used interchangeably for diagnosis and monitoring of treatment.