Elevated platelet-to-lymphocyte ratio is associated with stroke-associated pneumonia in acute ischemic stroke: a retrospective cohort study.

Background: Stroke-associated pneumonia (SAP) is a common and serious complication of acute ischemic stroke (AIS) that substantially worsens clinical outcomes. The platelet-to-lymphocyte ratio (PLR), an accessible composite index derived from routine complete blood counts, may reflect post-stroke immune imbalance. However, its role in predicting SAP in AIS patients remains unexplored. Methods: This retrospective cohort study included 1,745 patients with acute ischemic stroke (AIS) after systematic screening of 2,150 patients. After the original screening, 1,766 eligible patients remained; 21 additional patients with extreme PLR values (>1,000) were excluded. HbA1c missing values were imputed once using multiple imputation by chained equations (MICE) with a random forest estimator. PLR was calculated as platelet count divided by lymphocyte count and log2-transformed. Multivariable logistic regression, generalized additive modeling (GAM), and two-piecewise logistic regression were used to examine associations between PLR and stroke-associated pneumonia (SAP). Subgroup analyses were performed across seven clinical variables with interaction tested by likelihood ratio test. Predictive performance was evaluated by receiver operating characteristic (ROC) analysis and compared with C-reactive protein (CRP) and A2DS2 score using the DeLong test. Results: SAP occurred in 359 patients (20.6%). PLR was higher in patients with SAP than in those without SAP (median 136.17 vs. 113.69, Conclusion: Elevated PLR is associated with SAP in AIS patients, exhibiting a non-linear threshold-dependent relationship. Although standalone discriminatory performance is modest, PLR is universally available from routine blood counts and may serve as a cost-effective tool for early SAP risk stratification. Prospective multicenter validation is warranted.