Neutrophil-to-Lymphocyte Ratio in Predicting Severity in Acute Pancreatitis: A Systematic Review and Exploratory Meta-Analysis

Background: Early identification of patients at risk of severe acute pancreatitis (AP) remains clinically important. The neutrophil-to-lymphocyte ratio (NLR) is inexpensive, rapidly available, and has been investigated as a prognostic biomarker, but reported thresholds, measurement times, and target outcomes vary substantially. Methods: A systematic review with exploratory quantitative synthesis was conducted using PubMed/MEDLINE, Google Scholar, and Semantic Scholar. Adult studies evaluating admission or early-hospitalization NLR against severe AP, persistent organ failure, intensive care admission, pancreatic complications, mortality, or related adverse outcomes were eligible. Studies were grouped according to NLR timing, target outcome, exposure definition, and effect measure; statistically incompatible estimates were not pooled. Results: Of 149 records screened, 10 primary studies were included in qualitative synthesis and five contributed numerical estimates to graphical quantitative synthesis. Higher NLR was consistently associated with more severe disease. Study-specific AUROCs were 0.760 for admission NLR predicting persistent organ failure, 0.785 for 48-hour NLR predicting severe AP, and 0.998 for day-0 NLR distinguishing mild from combined moderately severe/severe AP. These estimates were not pooled because timing and target outcomes differed. Association estimates also remained separate: NLR ≥11 was associated with persistent organ failure (HR 1.37, 95% CI 1.00–1.89), NLR ≥10 with severe hypertriglyceridemia-induced AP (OR 6.71), and continuous admission NLR with severe AP (OR 3.78, 95% CI 2.83–5.06). Conclusion: NLR is a practical adjunct for early AP risk stratification, but current evidence does not support a universal threshold or single pooled prognostic effect. Prospective validation using standardized timing and outcomes is required.