Systemic pro-coagulatory and pro-inflammatory factors are critical factors in acute pulmonary embolism (APE). Recently the systemic immune-inflammation index (SII) has emerged as a new inflammatory and prognostic marker. We aimed to determine whether there is a relationship between SII and the severity of the APE. Methods. A total of 442 patients with APE, 202 women (45.7%) with an average age of 64 ± 16, were included in this retrospective observational study. APE severity was classified as massive (high risk), submassive (intermediate risk), and nonmassive (low risk). On admission, blood samples were collected for SII and other laboratory measurements. The SII was defined as platelet × neutrophil/lymphocyte counts. Results. SII levels were higher in patients with massive APE and gradually increased from nonmassive to massive APE (p < .001). SII was also significantly higher in patients with in-hospital death. Multivariable analysis showed that SII was an independent predictor for massive APE (Odds ratio 1.005 (95% CI 1.002-1.007), p < .001), together with C-reactive protein and cardiac troponin. In the receiver operating characteristic curve, the optimal cutoff value of SII to predict a massive APE was 1161, with 91% sensitivity and 90% specificity (area under the curve: 0.957). Conclusion. Our findings support an association between a higher SII level and a massive APE. As a simple biomarker, SII is an independent predictor of more severe disease in patients with APE. SII is a more powerful tool than traditional inflammatory markers for predicting the severity of disease in these patients.
Keywords: Acute pulmonary embolism; severity; systemic immune-inflammation index.