Limits of Detection in Acute-Phase Protein Biomarkers Affect Inflammation Correction of Serum Ferritin for Quantifying Iron Status among School-Age and Preschool-Age Children and Reproductive-Age Women

Abstract

Background: Standardized practices are needed in the analysis of inflammation biomarker values outside limits of detection (LODs) when used for inflammation correction of nutritional biomarkers. Objective: We assessed the direction and extent to which serum C-reactive protein (CRP) and α-1-acid-glycoprotein (AGP) values outside LODs (<0.05 mg/L and >4.0 g/L, respectively) affect inflammation regression correction of serum ferritin and compared approaches to addressing such values when estimating inflammation-adjusted ferritin and iron deficiency (ID). Methods: We examined 29 cross-sectional datasets from 7 countries with reproductive-age women (age 15-49 y) (n = 12,944), preschool-age children (age 6-59 mo) (n = 18,208), and school-age children (age 6-14 y) (n = 4625). For each dataset, we compared 6 analytic approaches for addressing CRP < 0.001). Conclusions: These findings demonstrate the need for standardized analyses of inflammation biomarker values outside LODs and suggest that random number single imputation may be a reliable and feasible alternative to MI for CRP