title: Comparison of isotopic and immunoenzymatic methods for folate and vitamin B12 determination.
abstract: BACKGROUND
  The objective of this study was to compare automated immunoenzymatic assay (IEA) with an isotopic reference method for determination of plasma folate, erythrocyte folate, and plasma vitamin B12 levels.
  
  
  METHODS
  Analytical performance including within-run and between-run imprecision was assessed on the automated IEA on the Access2 (Beckman Coulter, France). Folate and B12 levels determined routinely with a radioimmunoassay (RIA) (Simultrac, Diasorin, Italy) using EDTA samples (n=100) were compared to the Access2 IEA. To evaluate pre-analytical conditions, EDTA and heparinized plasma (n=56) from simultaneous samplings were used to compare folate and B12 levels via RIA and the Access2. In addition, discordant results were assayed by IEA on the Architect i2000 (Abbott, France).
  
  
  RESULTS
  Coefficient of variation for folate and B12 measurements on the Access2 ranged between 1.5% and 4.1%, respectively, for within-run assays, while between-run imprecision ranged from 4.8% to 9.3%, respectively. Comparison of RIA (x) and IEA on the Access2 (y) using EDTA samples showed a good correlation for plasma folate (y = 0.94x + 1.09; r2 = 0.83), acceptable correlation for erythrocyte folate (y = 0.65x + 137; r2 = 0.57) and discrepancy for B12 (y = 0.67x + 211; r2 = 0.37). This discordance for vitamin B12 was not observed when comparing RIA (x) and IEA on the Architect i2000 (y) (y = 0.74x + 40; r2 = 0.92) and disappeared when using heparinized samples for the Access2 (y = 0.85x + 7.05; r2 = 0.90).
  
  
  CONCLUSIONS
  Automated IEA appears to be a good alternative to RIA for the determination of folate and vitamin B12 but requires the use of an adequate anticoagulant.
authors.affiliation: Biochemistry Laboratory, CHRU Montpellier, University Montpellier I, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Badiou
authors.forename: Sophie
authors.initials: S
authors.lastname: Bariolet
authors.forename: Chrisléne
authors.initials: C
authors.lastname: Laurens
authors.forename: Nadine
authors.initials: N
authors.lastname: Aillaud
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Bargnoux
authors.forename: Denis
authors.initials: D
authors.lastname: Mariano-Goulart
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Dupuy
authors.forename: Jean Paul
authors.initials: JP
authors.lastname: Cristol
mesh_terms: D004912:Erythrocytes / Q000737:chemistry; D005492:Folic Acid / Q000032:analysis / Q000097:blood*; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods*; D016014:Linear Models; D011863:Radioimmunoassay / Q000379:methods*; D015203:Reproducibility of Results; D014805:Vitamin B 12 / Q000097:blood*
chemical_list: D005492:Folic Acid; D014805:Vitamin B 12