Comparison of the automated AxSYM and ADVIA centaur immunoassays for homocysteine determination

A new fully automated chemiluminescence assay for total homocysteine (tHcy) determination (ADVIA Centaur homocysteine, Bayer) was evaluated in comparison with a previously established fluorescence polarization assay (AxSYM homocysteine, Abbott). Linearity could be demonstrated in a concentration range up to 50 micromol/l for both methods. The detection limit was 0.92 micromol/l for the AxSYM and 0.61 micromol/l for the ADVIA Centaur analyzer. Within-run coefficients of variation (%CV) ranged from 1.7% to 1.8% for the AxSYM, and from 2.2% to 2.7% for the ADVIA Centaur analyzer, total CV ranged from 2.5% to 3.5% for the AxSYM, and from 3.6% to 4.5% for the ADVIA Centaur analyzer. Passing and Bablock regression analysis of 180 samples with the AxSYM assay as reference method revealed an intercept of -0.41 micromol/l (95% CI -1.17 to 0.20 micromol/l) and a slope of 1.11 (95% CI 1.05 to 1.18), the Bland-Altman difference plot showed a mean difference of -0.9 micromol/l between tHcy measurements with wide 95% limits of agreement (-3.6 to 1.7 micromol/l). At thresholds of 10 and 15 micromol/l there was a considerable proportion of discordant classifications of study subjects by the AxSYM and ADVIA Centaur method. When evaluating case-control status for vascular disease both assays showed similar characteristics (i.e., significant difference of tHcy in 71 CAD patients and 109 control subjects, and non-significant odds ratios for tHcy in the multivariate model). In conclusion, both methods are reliable for routine tHcy determination in clinical laboratories, as they are fast and completely automated systems with good accuracy and precision allowing sample random access, automatic dilution and stored calibration capabilities. However, results of both assays may not be used interchangeably since the ADVIA Centaur method tends to overestimate tHcy values compared to the AxSYM method.