Abstract
Background: Homocysteine is an amino acid that has been linked to an increased risk of coronary artery disease and stroke. A recombinant enzymatic cycling assay for homocysteine was evaluated using a Roche Modular Analytics P800 chemistry analyzer.
Methods: Bound homocysteine is released by disulfide reduction and combined with serine to form
l-cystathionine that is degraded by cystathionine β-lyase into homocysteine, pyruvate, and ammonia. Pyruvate is converted to lactate and the amount of NAD
+ produced is directly proportional to the concentration of homocysteine. The limit of detection (LOD), linearity, imprecision, method comparison, reference interval and susceptibility to common interferences were assessed.
Results: The limit of detection was 0.31 μmol/l. The method was linear from 1 to 100 μmol/l with a maximum deviation from the target concentration of <10%. The total imprecision was <5.4% for homocysteine concentrations between 11.4 and 39.4 μmol/l. Method comparison was performed using an immunoassay on the ADVIA Centaur as the comparison method. Deming regression analysis gave a slope of 1.00, intercept of −0.75 and
r=0.992. The mean bias relative to the ADVIA Centaur method was −0.9 μmol/l with limits of agreement of −5.0 and +3.5 μmol/l. The reference interval was 4.7 to 12.7 μmol/l.
Conclusions: This enzymatic assay for homocysteine provides acceptable performance on the Modular Analytics P800 analyzer.