title: Homocysteine measurement by Vitros Microtip homocysteine assay.
abstract: BACKGROUND
  Elevated circulating total homocysteine is an independent vascular risk factor. Enzymatic homocysteine measurements represent an alternative to HPLC- or immunochemistry-based assays, suitable for automation. Here, we report on analytical performance of a commercial cystathionine beta-synthase-based assay, for use on Vitros automated analyzers.
  
  
  METHODS
  Linear range, limit of detection and analytical sensitivity were inferred from duplicate measurements of homocystine standard solutions (1-65 micromol/L). Imprecision was assessed using commercial controls according to NCCLS EP5-A2 and accuracy using NIST-SRM1955 reference material. Agreement with a clinically validated HPLC method was examined on 207 patient samples.
  
  
  RESULTS
  The enzymatic assay was linear from 1 to 90 micromol/L homocysteine. Total (within-day) imprecision ranged from 4.5 (3.9)% to 2.8 (1.6)% at homocysteine 9.7-43.2 micromol/L. Accuracy was acceptable at 8.9 and 17.7 micromol/L homocysteine, with +6.4% and -1.2% bias, respectively, but showed substantial negative bias (-20.1%) at 4.0 micromol/L. High triglycerides (19.8 micromol/L) negatively interfered. The enzymatic method was slightly less sensitive than the HPLC method (limit of detection 0.7 and 0.2 micromol/L, respectively) but correlated well with the latter (r2=0.9997, slope=1.04, intercept=-0.66 micromol/L) and was more precise (p<0.05).
  
  
  CONCLUSIONS
  The Vitros homocysteine assay met the CLIA Desirable Analytical Quality Specifications at homocysteine > or = 9 micromol/L. Its analytical performance and suitability for automation make the Vitros assay an analytically acceptable alternative to HPLC-based methods.
authors.affiliation: Department of Clinical Chemistry and Radioimmunology, Universitair Ziekenhuis Brussel, Brussels, Belgium. geert.martens@uzbrussel.be
authors.forename: Geert A
authors.initials: GA
authors.lastname: Martens
authors.forename: Joeri
authors.initials: J
authors.lastname: De Nayer
authors.forename: Dieter
authors.initials: D
authors.lastname: De Smet
authors.forename: Pedro
authors.initials: P
authors.lastname: Couck
authors.forename: Frans
authors.initials: F
authors.lastname: Gorus
authors.forename: Erik
authors.initials: E
authors.lastname: Gerlo
mesh_terms: D016477:Artifacts; D002851:Chromatography, High Pressure Liquid; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D006710:Homocysteine