Nonlinear association between baseline neutrophil-to-lymphocyte ratio and severe acute pancreatitis in the MIMIC-IV database

This study evaluated the association between baseline neutrophil-to-lymphocyte ratio (NLR) and severe acute pancreatitis (SAP) in patients with acute pancreatitis (AP) using MIMIC-IV data. Adult patients with index AP admission and NLR measured within 24 h were included. The primary outcome was severe AP, defined by the Revised Atlanta Classification as Modified Marshall organ failure persisting beyond 48 h; in-hospital mortality was the key secondary outcome, with prolonged ICU and hospital stay evaluated as additional secondary outcomes. Mechanical ventilation and vasopressor use were retained as descriptive endpoints because they contributed to the EHR-based operationalization of organ dysfunction. Multivariable logistic regression and restricted cubic spline (RCS) analyses were performed with adjustment for age, sex, race/ethnicity, etiology, and APACHE II score; subgroup analyses were also conducted. Among 1,044 patients, 200 (19.2%) developed severe AP and 106 (10.2%) died in hospital; ln(NLR) was independently associated with severe AP (OR = 1.329, 95%CI:1.129–1.566, p < 0.001). RCS revealed a significant nonlinear relationship ( p < 0.001), with a steeper increase in the odds of severe AP around NLR values of 8–9 and a flattening thereafter. High NLR was associated with higher odds of in-hospital mortality compared with low NLR (OR = 2.300, 95%CI: 1.340–3.949, p = 0.003), and continuous ln(NLR) was also associated with mortality (OR = 1.420, 95%CI: 1.129–1.785, p = 0.003), although the nonlinear component was not significant for mortality ( p = 0.063). Baseline NLR shows a nonlinear association with severe AP in MIMIC-IV, with a steeper increase in the odds of severe AP around NLR values of 8–9. NLR may serve as an accessible early risk stratification tool, though external validation is needed.