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 alpha-1-acid glycoprotein (AGP) have allowed their application to micronutrient surveys conducted in low-resource countries for similar to 2 decades. Objectives: We conducted a comparison between the ELISA and reference-type assays used in the US NHANES. 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 aged 6-59 mo; 100 serum samples from nonpregnant women) for Fer, sTfR, CRP and AGP. We compared the combined data sets with 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 as follows: 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 as follows: 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. Conclusions: 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.

Automated summary

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. However, the lack of standardization in sTfR assays led to a significant systematic difference.