Comparison of Inflammation Adjustment Strategies for Retinol-binding Protein in Acute and Convalescent Serum of Patients with Acute Febrile Illness in Guayaquil, Ecuador (P10-095-19)

Objectives 1. Assess serum retinol-binding protein (RBP) among clinical participants at two time points: during the onset of acute febrile illness and again during the convalescent recovery phase. 2. Apply and compare several inflammation adjustment strategies for determining vitamin A status. Methods Patients presenting with acute febrile illness were enrolled. Participants were asked to return for a follow-up convalescent visit 2–4 weeks later. Comprehensive demographic and clinical information along with blood samples were collected at both visits. RBP, C-reactive protein (CRP), and alpha-1-acid glycoprotein (AGP) were measured by ELISA, (R&D Systems, Inc., Minneapolis, MN), and pro-inflammatory cytokines were measured by magnetic bead multiplex assay, (EMD Millipore Corporation, Billerica, MA). Continuous RBP was adjusted using the Thurnham correction factor (TCF), the BRINDA regression correction (BRC), and the CRP-only adjustment factor (CAF). An interleukin 6 (IL-6) regression model was also applied to adjust RBP based on IL-6 concentrations for participants with CRP ≥5 mg/L. Adjusted RBP concentrations were compared between paired visits using non-parametric paired Wilcoxon signed-rank tests, and p values <0.05 were considered significant. Results Blood samples were collected from 18 participants during acute and convalescent phase visits. The unadjusted median (quartile 1-quartile 3) RBP concentration (µmol/L) during the acute visit, 1.02 (0.90–1.21), was lower than the convalescent visit, 1.57 (1.26–1.75), P = 0.0004. After applying the TCF, BRC, and CAF, median RBP between visits differed significantly, similar to the unadjusted RBP. RBP adjusted using the IL-6 regression model was not significantly different between paired visits 1 and 2, 1.40 (1.11–1.76) and 1.62 (1.26–1.97) respectively, P = 0.12. Conclusions Circulating unadjusted RBP concentrations were significantly lower in participants during the acute illness phase compared to the convalescent recovery phase. Under the assumption that underlying vitamin A status remains constant during a 2–4 week period, adjusting RBP for IL-6 in participants with CRP ≥5 mg/L was the only strategy in which adjusted RBP did not differ significantly between paired visits. Funding Sources NIH National Institute of Biomedical Imaging and Bioengineering, NIH Office of Research on Women's Health.