Deficiencies of vitamin A, iron and iodine affect a significant portion of the world’s population and are often associated with adverse health outcomes, particularly among pregnant women and children. Efforts to characterize deficiency patterns have been hampered by a lack of measurement tools appropriate for large-scale use. Since many of these micronutrients are not easily measured directly, reliable proxy markers indicative of deficiency status have been identified and widely adopted. Inflammation or infection marker levels must be measured at the same time, as these affect the levels of vitamin A and iron status markers. Furthermore, malaria infection is known to deplete iron levels, thus screening for malaria is also recommended. We previously developed a prototype multiplexed immunoassay for the simultaneous measurement of five markers relevant to assessing vitamin A, iron status and infection; retinol binding protein, soluble transferrin receptor, ferritin, a-1-acid glycoprotein and C-reactive protein. Here we present an improved version of the immunoassay which has also been expanded to include measurement of the biomarkers for iodine deficiency (thyroglobulin) and malaria infection (Histidine Rich Protein II).
Using affordable technology from Quansys Biosciences, antibodies are coated in seven discrete regions of the well of a microtiter plate and the seven analytes are assayed in a single volume of sample. A control standard was developed for the assay that reflected the clinical range of each biomarker being assayed. Assay performance was evaluated by comparing the multiplexed and conventional monoplex assay results for plasma from 170 adult US volunteers.
The new multiplex immunoassay and established conventional assay methods showed high correlation for all analytes tested (an average of 0.77), improving on the values observed with the original 5-plex plate. Use of a control standard specifically designed for the multiplex assay in place of a commercially available standard allowed for more accurate quantitation of each analyte.
This 7-plex micronutrient assay has excellent potential for use as a cost effective tool for population surveillance of vitamin A, iron and iodine deficiencies as well as malarial parasitemia infectivity rate. The assay is easy to use, rapid, and accurate and needs only a low cost reader and basic equipment present in most reference laboratory settings.