Association of neutrophil-to-prognostic nutritional index ratio with long-term mortality in acute myocardial infarction from Chinese and US cohorts

Background Despite advancements in reperfusion strategies, patients with acute myocardial infarction (AMI) face significant risks of long-term mortality. Systemic inflammation and nutritional/immune depletion synergistically impact prognosis. This study investigated the prognostic value of the neutrophil count to prognostic nutritional index ratio (NPNR)—a novel composite index reflecting inflammatory burden and nutritional reserves—in AMI patients. Methods This dual-cohort study included 2020 patients from the NOAFCAMI-SH registry in China and 1,433 patients from the MIMIC-IV database in the USA. The primary endpoint was all-cause mortality; the secondary endpoint was cardiovascular mortality. Associations were analyzed using Kaplan-Meier curves, Cox regression, and restricted cubic splines. Results During a median 2.5-year follow-up in the discovery cohort, 285 all-cause and 234 cardiovascular deaths occurred. Higher NPNR levels correlated with myocardial injury and lower LVEF. Kaplan-Meier analysis showed significantly worse survival with elevated NPNR ( P < 0.001). In fully adjusted models, NPNR independently predicted all-cause (HR: 2.59, 95% CI: 1.21–5.54) and cardiovascular mortality (HR: 2.87, 95% CI: 1.34–6.15). Compared to the lowest tertile, patients in the highest NPNR tertile had a 2.19-fold higher risk of all-cause mortality (HR: 2.19, 95% CI: 1.55–3.09) and a 2.36-fold higher risk of cardiac death (HR: 2.36, 95% CI: 1.60–3.48). This was validated in the MIMIC-IV cohort (HR:1.91 for 1-year mortality). The association was particularly strong in patients aged ≥65 years. Adding NPNR to a baseline clinical model significantly improved overall discrimination (C-statistic: 0.807–0.811, P = 0.011) and risk reclassification for mortality (continuous NRI = 0.368, IDI = 0.011; both P = 0.013). Conclusion NPNR is a robust, independent predictor of long-term all-cause and cardiac mortality in AMI patients, validated in the external MIMIC-IV cohort. This simple biomarker effectively aids in risk stratification.