Analysis of the association between the neutrophil-to-lymphocyte ratio (NLR) and liver injury complicating acute pancreatitis: a retrospective study.

BACKGROUND: Acute pancreatitis is frequently complicated by acute liver injury (ALI), which exacerbates systemic inflammation and increases mortality. Early identification of high-risk patients remains challenging. The neutrophil-to-lymphocyte ratio (NLR) is a simple marker of systemic inflammation, but its association with ALI in acute pancreatitis is unclear. OBJECTIVES: To investigate the association between NLR and ALI in acute pancreatitis and evaluate its predictive value. METHODS: Clinical data from 581 acute pancreatitis inpatients (2021-2025) were retrospectively analyzed. Multivariate logistic regression, generalized additive models, subgroup analyses, interaction tests, and ROC curves were used. RESULTS: ALI occurred in 37.7% of patients. After adjustment, each one-unit NLR increase raised ALI risk by 11% (OR = 1.11, 95% CI: 1.08-1.14, P < 0.001). The highest NLR quartile had a 5.42-fold higher risk than the lowest. A non-linear threshold was identified at NLR = 2.92: risk rose sharply below this point (OR = 6.55) and more gradually above it (OR = 1.07), suggesting that even a mild NLR elevation may signal early liver injury risk. NLR alone predicted ALI with AUC = 0.688 (cutoff 8.26, sensitivity 59.4%, specificity 68.0%). Adding CRP and gallstones improved AUC to 0.756 (sensitivity 65.8%, specificity 76.2%), indicating that combining inflammatory markers with etiological factors enhances predictive accuracy. CONCLUSION: NLR independently predicts ALI in acute pancreatitis with a non-linear threshold effect. NLR ≥ 2.92 can serve as an early warning signal to initiate enhanced liver function monitoring, while NLR ≥ 8.26 identifies patients at high risk. Combining NLR with other readily available indicators significantly improves predictive performance and may facilitate early clinical decision-making.