Comparison of the Abbott IMx (R) and a high-performance liquid chromatography method for measuring total plasma homocysteine

The determination of the total concentration of plasma homocysteine is of i nterest in a variety of clinical circumstances, especially, in the evaluati on of the risk of cardiovascular disease. However, most of the methods avai lable to date, many of them chromatographic, are not well suited for the ma jority of clinical laboratories. Several automated methods are now or will be, shortly, commercially available. We have compared one of them, the fluo rescence polarization immunoassay (FPIA) adapted to the IMx(R) analyzer (Ab bott Laboratories), with the high-performance liquid chromatography (HPLC) method with fluorescent detection currently used in our laboratory. The res ults show that the FPIA-IMx(R) method is less imprecise and slightly more s ensitive than the HPLC. The comparison of 67 clinical plasma specimens indi cated that there is a proportional error disagreement between FPIA-IMx(R) a nd HPLC (FPIA = 1.19 HPLC + 0.92; confidence region for slope and y-interce pt were, respectively, from 1.06 to 1.31 and from -0.06 to 2.32). The natur e of this error is not explained by the experiments performed to study the inaccuracy of both methods, which included the investigation of dilution pa rallelism, analytical recovery and cross-reactivity. The different results of homocysteine concentration obtained with FPIA-IMx(R) and HPLC must be ta ken into account when a change of methodology is under consideration.