Persistent elevation of serum LBP, IL-23 and IL-6 in infliximab-maintained Crohn's disease: a case–control study from Iraq with the serum LBP/albumin ratio as a novel composite biomarker

Abstract

Background and aims Serum biomarkers that track mucosal inflammation in Crohn's disease (CD) beyond C-reactive protein (CRP) remain limited, particularly in Middle Eastern populations and in patients maintained on infliximab (IFX). We evaluated serum lipopolysaccharide-binding protein (LBP), interleukin-23 (IL-23) and interleukin-6 (IL-6) in active and IFX-maintained Iraqi CD patients versus healthy controls, and investigated the LBP-to-albumin ratio (LBP/Alb) as a novel composite biomarker. Methods In this cross-sectional case–control study (27 October 2025–25 March 2026) at Al-Najaf Gastrointestinal Tract Hospital, Iraq, 117 adults were enrolled: active CD (n = 32), IFX-CD (≥ 12 months maintenance; n = 35) and healthy controls (HC; n = 50). Serum LBP, IL-23 and IL-6 were measured by ELISA (BT Lab, Shanghai); CRP and albumin were measured on an SMT-120 analyser (Seamaty) in fixed-time mode. Activity was scored by the Harvey–Bradshaw Index (HBI); nutritional risk by MUST. Results LBP, IL-23 and IL-6 were significantly higher in both active CD and IFX-CD than in HC (all P < 0.001 after Bonferroni adjustment); pairwise differences between active CD and IFX-CD were not significant. IL-6 (AUC 0.982) and IL-23 (AUC 0.969) outperformed CRP (AUC 0.667) for discriminating all CD from HC. A combined IL-23 + IL-6 + CRP model reached AUC 0.995 (McFadden To address the possibility of overfitting and optimism in the diagnostic estimates, ROC performance was additionally evaluated by 5-fold stratified cross-validation in which standardisation and model fitting were performed within each training fold and applied to the held-out fold; cross-validated AUCs are reported with bootstrap 95% confidence intervals. Given the case–control design and the single-centre sample, these internal estimates are not a substitute for external validation, which remains necessary before any diagnostic application.R2 = 0.812). LBP/Alb correlated most strongly with HBI (ρ = 0.41), MUST (ρ = 0.50) and BMI (ρ = −0.46; all P < 0.001). Conclusions Serum LBP, IL-23 and IL-6 are markedly elevated in Iraqi CD patients and remain elevated during IFX maintenance, suggesting residual subclinical inflammation not captured by CRP alone. The LBP/Alb ratio is a promising accessible composite biomarker integrating bacterial-translocation and nutritional signals.