Performance characteristics of a recombinant enzymatic cycling assay for quantification of total homocysteine in serum or plasma.
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 beta-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 micromol/l. The method was linear from 1 to 100 micromol/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 micromol/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 micromol/l with limits of agreement of -5.0 and +3.5 micromol/l. The reference interval was 4.7 to 12.7 micromol/l.


CONCLUSIONS
This enzymatic assay for homocysteine provides acceptable performance on the Modular Analytics P800 analyzer.
Roberts
Richard F
RF
ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT, USA.
Roberts
William L
WL
D001331:Automation; D001774:Blood Chemical Analysis / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D004798:Enzymes; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D007202:Indicators and Reagents; D009243:NAD / Q000032:analysis / Q000737:chemistry; D011994:Recombinant Proteins; D012680:Sensitivity and Specificity
D004798:Enzymes; D007202:Indicators and Reagents; D011994:Recombinant Proteins; D006710:Homocysteine; D009243:NAD