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Comparison of Isotopic and Immunoenzymatic Methods for Folate and Vitamin B12 Determination by Stéphanie Badiou, Sophie Bariolet, Chrisléne Laurens, Nadine Aillaud, Anne-Sophie Bargnoux, Denis Mariano-Goulart, Anne-Marie Dupuy, Jean Paul Cristol

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 radio-immunoassay (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.

DOI: Clin. Lab. 2010;56:547-552