ABSTRACT
Objectives: Deficiencies of vitamin A and iron affect a significant portion of the world's population, and efforts to characterize deficiency patterns have been hampered by a lack of measurement tools appropriate for large-scale use. Since vitamin A and iron are not easily measured directly, reliable proxy markers indicative of deficiency status have been identified and widely adopted. Inflammation or infection must be assessed at the same time, as these affect vitamin A and iron status markers. To address these technical challenges, we developed a multiplex immunoassay method for simultaneous measurement of five markers relevant to assessing vitamin A and iron status and infection: retinol binding protein, soluble transferrin receptor, ferritin, alpha-1-acid glycoprotein and c-reactive protein. Methods: Using affordable technology from Quansys Biosciences, antibodies are coated in five discrete regions of the well of a microtiter plate and the five analytes are assayed in a single volume of sample. Assay performance was evaluated by comparing multiplex and conventional assay results for plasma from 72 US volunteers. Results: Results of the new and established conventional assay methods were highly correlated (0.606 to 0.991, p<.0001). Inter-assay imprecision for the multiplex panel varied from 1% to 8%, and all samples fell within the limits of quantification for all assays at a single dilution. Absolute values given by the multiplex and conventional assays differed, indicating a need for further work to devise a new calibration curve. Conclusions: This multiple micronutrient assay has excellent potential for use in population assessment of vitamin A and iron deficiencies.