Comparison study between RBC folate measured by microbiologic assay and Immulite 2000 immunoassay

Significant inter‐laboratory differences exist in values obtained for RBC folate (RBF). The objective of this methods comparison study was to generate a conversion equation that describes the relationship between RBF measured by the Immulite 2000 immunoassay and the microbiologic assay (MA). Blood was drawn from 152 healthy participants in Toronto, Canada. Folate concentrations were determined by MA (chloramphenicol‐resistant microorganism [L. Rhamnosus], calibrated with 5‐methyltetrahydrofolate) at The Hospital for Sick Children and by the Immulite 2000 immunoassay at the Health Canada Canadian Health Measures Survey (CHMS) laboratory. A Pearson's coefficient, r, of 0.67 guided the decision to use weighted Deming regression, which accounts for random error of both X and Y and controls for proportional bias. The final weighted Deming regression model was as follows: Predicted microbiologic assay = −22.95 + 0.81*Immunoassay. For validation, the whole sample was randomly split into two groups: 1) estimation 2) validation. The same mean absolute percentage error was obtained in the validation group as in the entire sample set (23%), indicating robustness in the precision of the model's predicted values. This equation will be used to compare the RBF data from the CHMS to the US NHANES (measured by Immulite 2000 immunoassay and MA, respectively). Grant Funding Source : Canadian Institutes for Health Research Fellowship (180375) to C.K.C and Operating Grant (218776) to M.S.T, D.L.O and C.K.C