Abstract Body (Do not enter title and authors here): Background.
The neutrophil-to-lymphocyte ratio (NLR) is a marker of systemic inflammation associated with adverse cardiovascular outcomes. Its prognostic role in patients with diabetes mellitus (DM) undergoing percutaneous coronary intervention (PCI) is unknown.

Aims.
To investigate the prognostic impact of NLR in patients with and without DM undergoing PCI.

Methods.
We retrospectively evaluated consecutive patients undergoing PCI at a large tertiary center between 2012 and 2022. Quartiles of NLR were derived in the overall population, and patients were stratified according to the presence of DM. Within each group, we estimated the risk of adverse events with a multivariable Cox regression model using the lowest NLR quartile as a reference. The primary endpoint was major adverse cardiovascular events (MACE), a composite of all-cause death, myocardial infarction (MI), or stroke. Secondary endpoints were MACE individual components, target vessel revascularization (TVR), bleeding and acute kidney injury (AKI).

Results.
A total of 7,287 patients were included (47.7% with DM). DM patients had more comorbidities and higher baseline hs-CRP levels. Overall, patients with elevated NLR exhibited multi-vessel disease with moderate to severe calcification, thus requiring more complex PCI. At 1 year, among DM patients, the 4^th quartile had a higher crude risk of MACE compared to the 1^st quartile, albeit attenuated after adjustment (p=0.059). This difference was mainly driven by MI rates occurring in 6.0% vs 3.8% respectively (adjHR 1.70, 95% CI 1.01-2.87; P=0.045). Non-DM patients in the highest NLR quartile had increased rates of MACE (adjHR 2.12, 95% CI 1.29-3.49; P=0.003) primarily due to all-cause mortality (adjHR 3.04, 95% CI 1.49-6.20; P=0.002) after adjustment. Regarding secondary endpoints, elevated NLR correlated with higher incidence of (i) bleeding and AKI in both groups and (ii) TVR only in non-DM patients (Figure 1).

Conclusions.
Our results suggest that patients undergoing PCI with a higher NLR experience worse clinical outcomes regardless of DM status. This was due to more MI in DM group and higher all-cause mortality in non-DM group. Higher NLR was also associated with an increased risk of bleeding and AKI.