Role of Systemic Immune-Inflammatory Index and WBC Differential in Predicting the Severity of Acute Pulmonary Embolism: A Single-Center Observational Study at King Fahad Specialist Hospital, Buraydah, Saudi Arabia

Background Early identification of high-risk pulmonary embolism (PE) is crucial for improving patient outcomes. The systemic immune‑inflammatory index (SII) has emerged as a potential biomarker of thromboinflammatory activity. This study aimed to assess the roles of SII and white blood cell (WBC) differentiation in predicting the severity of acute PE (APE). Methods This was a retrospective study of patients with APE admitted to King Fahad Specialist Hospital in Saudi Arabia from 2022 to 2025. Data included demographics, chronic diseases, and clinical features. Furthermore, vital signs, oxygen saturation, complete blood count with differential, echocardiography, and computed tomography angiography results at admission, and mortality rate were collected. All patients were classified according to severity using the Pulmonary Embolism Severity Index (PESI) score and PE risk stratification as massive, submassive, or non-massive. All statistical analyses were performed using IBM SPSS Statistics for Windows, version 26 (IBM Corp., Armonk, New York, United States). Results Among the 166 patients with APE (mean age: 57.1 years) included in this study, 93 patients (56%) were female, and hypertension and diabetes were the most common comorbidities, with 73 (44%) and 61 (36.7%) having them, respectively. Levels of inflammatory markers (WBC and neutrophils) and cardiac biomarkers (troponin) are markedly elevated in patients with massive PE. Receiver operating characteristic analysis showed that neutrophil count (area under the curve: 0.766), WBC (0.736), and SII (0.656) had good predictive accuracy for massive PE, but platelet count was not a useful predictor (p = 0.089). PESI scores demonstrated a strong association with PE severity, increasing stepwise from non‑massive to massive PE (78.6 ± 37.4 vs. 84.2 ± 32.9 vs. 136.5 ± 54.9; p < 0.001). Conclusion Elevated SII, neutrophil count, and WBC count were significantly associated with massive PE and adverse outcomes. These markers offer value for early risk stratification and may enhance clinical decision-making in the management of APE.