Determination of total homocysteine in plasma: comparison of the Abbott IMx immunoassay with high performance liquid chromatography

Abstract

BACKGROUND AND OBJECTIVES: The aim of this study was to compare the performance of a commercially available IMx immunoassay with that of a reversed-phase high performance liquid chromatography (HPLC) method for measuring plasma total homocysteine (tHcy). METHODS: The levels of tHcy before and after oral methionine loading (ML) were measured in 135 healthy subjects and 39 patients scheduled for routine tHcy determination. The IMx method uses fluorescence polarization immunoassay (FPIA) technology. The HPLC-method includes derivatization with ABD-F and post-column fluorescence detection. RESULTS: The imprecision was very low with both methods for both normal (11 mmol/L) and high (29 mmol/L) tHcy levels. The within and between-run coefficients of variation were < 5%. Both methods were able to discriminate between similar concentrations of tHcy both at normal and moderately high levels. There was a good correlation between measurements obtained with the two methods (r = 0.985, p = 0.001). The mean levels of tHcy measured with the IMx assay tended to be slightly higher than those with the HPLC both in the fasting state (mean difference = 0.8 mmol/L) and after ML (5.3 mmol/L). However only the difference in post-ML levels was statistically significant (p < 0.001). The percentage of patients with hyperhomocysteinemia identified with the two methods was similar. INTERPRETATION AND CONCLUSIONS: The IMx method compares well with an established HPLC method for measurement of fasting tHcy plasma levels.