The pre-procedural neutrophil to lymphocyte ratio (N/L) is associated with adverse outcomes among patients with coronary artery disease but its prognostic value in ST-segment elevation myocardial infarction (STEMI) has not been fully investigated. This study evaluated the relations between pre-procedural N/L ratio and the in-hospital and long-term outcomes in STEMI patients undergoing primary percutaneous coronary intervention (PCI).

A total of 682 STEMI patients presented within the first 6 h of symptom onset were enrolled and stratified according to tertiles of N/L ratio based on the blood samples obtained in the emergency room upon admission.

The mean follow-up period was 43.3 months (1–131 months). In-hospital in-stent thrombosis, non-fatal myocardial infarction, and cardiovascular mortality increased as the N/L tertile ratio increased (p < 0.001, p < 0.001, p = 0.003, respectively). Long-term in-stent thrombosis, non-fatal myocardial infarction and cardiovascular mortality also increased as the N/L ratio increased (p < 0.001, p < 0.001, p = 0.002, respectively). On multivariate analysis, N/L ratio remained an independent predictor for both in-hospital (OR 1.189, 95% CI 1.000–1.339; p < 0.001) and long-term major (OR 1.228, 95% CI 1.136–1.328; p < 0.001) adverse cardiac events.

The N/L ratio was an independent predictor of both in-hospital and long-term adverse outcomes among STEMI patients undergoing primary PCI. Our findings suggest that this inexpensive, universally available hematological marker may be incorporated into the current established risk assessment model for STEMI.