Abstract
We evaluated the precision, linearity and accuracy of the Abbott IMxTM and Bio-Rad (Axis) homocysteine assays. Both assays make use of S-adenosylhomocysteine hydrolase and excess adenosine, to convert homocysteine to S-adenosylhomocysteine (SAH). A monoclonal anti-SAH antibody is then used to quantify SAH. The IMx assay measures the fluorescence polarization of a conjugated SAH analogue for the final analytical step, whereas the Bio-Rad method uses a microplate enzyme immunoassay (EIA) employing an anti-mouse antibody-peroxidase conjugate. The Abbott procedure is completely automated whereas the Bio-Rad EIA is performed manually. Between-run coefficient of variation using commercial controls was 2·6% at 7 μmol/L, 2·5% at 13 μmol/L and 1·7% at 24 μmol/L for the Abbott method, and 19·7% at 6·4 μmol/L, 15·9% at 11·0 μmol/L and 14·5% at 23·4 μmol/L for the Bio-Rad method. Both assays correlated well with a high-performance liquid chromatography (HPLC) procedure for homocysteine: Bio-Rad EIA=1·03HPLC + 1·0 μmol/L, r=0·98, sy/x =0·51; Abbott IMx=1·02 HPLC + 0·7 μmol/L, r=0·99, sy/x =0·33. Both methods were linear up to 50 mol/L homocysteine. The IMx assay had superior precision as well as the technological advantage of being completely automated. Both immunoassays exhibited greatly improved throughput compared with our existing HPLC method.