Review of the magnitude of folate and vitamin B12 deficiencies worldwide.
To the Editor: Recently, several new nonisotopic protein-binding folate assays have become available. We have studied the AxSYM folate assay (Abbott Laboratories, Abbott Park, IL), in which folate is quantified by measurement of unoccupied binding sites on the folate-binding protein (1 ). The calibrators for the assay cover the range 0–45 nmol/L. In the absence of an internationally accepted reference method or material (2 ), we have compared the performance of the AxSYM method with two methods commonly used nationally and internationally, namely the SimulTrac-SNB (ICN