The VitMin Lab Sandwich-ELISA Assays for Iron and Inflammation Markers Compared Well with Clinical Analyzer Reference-type Assays in Subsamples of the Nepal National Micronutrient Status Survey.

BACKGROUND The low cost and small specimen volume of the VitMin Lab ELISA assays for serum ferritin (Fer), soluble transferrin receptor (sTfR), C-reactive protein (CRP), and α-1-acid glycoprotein (AGP) allowed their application to micronutrient surveys conducted in low-resource countries for ∼2 decades. OBJECTIVE We conducted a comparison between the ELISA and reference-type assays used in the US National Health and Nutrition Examination Survey. METHODS Using the Roche clinical analyzer as a reference, we measured random subsets of the 2016 Nepal National Micronutrient Status Survey (200 serum samples from children 6-59 mo; 100 serum samples from non-pregnant women) for Fer, sTfR, CRP, and AGP. We compared the combined data sets to the ELISA survey results using descriptive analyses. RESULTS The Lin's concordance coefficients between the 2 assays were ≥ 0.89 except for sTfR (Lin's rho = 0.58). The median relative difference to the reference was: Fer -8.5%, sTfR 71.2%, CRP -19.5%, and AGP -8.2%. The percentage of VitMin samples agreeing within ± 30% of the reference was: Fer 88.5%, sTfR 1.70%, CRP 74.9%, and AGP 92.9%. The prevalence of abnormal results was comparable between the 2 assays for Fer, CRP, and AGP, and for sTfR after adjusting to the Roche assay. Continued biannual performance (2007-2019) of the VitMin assays in CDC's external quality assessment program (6 samples/y) demonstrated generally acceptable performance. CONCLUSION Using samples from the Nepal survey, the VitMin ELISA assays produced mostly comparable results to the Roche reference-type assays for Fer, CRP, and AGP. The lack of sTfR assay standardization to a common reference material explains the large systematic difference observed for sTfR, which could be corrected by an adjustment equation pending further validation. This snapshot comparison together with the long-term external quality assessment links the survey data generated by the VitMin Lab to the Roche assays used in NHANES.