The predictive value of the systemic immune-inflammation index in chronic thromboembolic pulmonary hypertension

The systemic immune-inflammation index (SII) is associated with the severity and progression of vascular disorders. However, the relationship between SII and chronic thromboembolic pulmonary hypertension (CTEPH) remains unclear. This study aimed to investigate for the first time the predictive value of SII for the development of CTEPH in patients with a history of unprovoked acute pulmonary embolism (PE). This retrospective case-control study included 62 patients with unprovoked acute PE for the first time. Thirty patients with CTEPH and 32 without CTEPH were compared in terms of baseline and follow-up clinical, echocardiographic, and laboratory parameters obtained at least 3 months after the index event. Univariate and multivariate logistic regression analyses were performed to determine predictors of CTEPH. The diagnostic performance of the SII was evaluated using receiver operating characteristic curve analysis. Among the baseline laboratory parameters related to SII, only platelet count (308 [237-339] vs 259 [207-283], P = .028) was significantly higher in the CTEPH group, whereas SII did not differ significantly between the groups. During follow-up beyond 3 months, neutrophil count (5.4 [3.6-6.4] vs 4 [3.3-4.8], P = .01), platelet count (313 [219-376] vs 251 [201-295], P = .02), and SII (1614 [607-2147] vs 566 [417-727], P < .001) were significantly higher, whereas lymphocyte count (1.4 ± 0.5 vs 1.9 ± 0.5, P < .001) was significantly lower in the CTEPH group. Multivariate logistic regression analysis demonstrated that the SII was an independent predictor of CTEPH (odds ratio 1.003 [1.000-1.005], P = .02). Receiver operating characteristic curve analysis showed that the SII had moderate diagnostic performance for predicting CTEPH (area under the curve = 0.797; 95% confidence interval, 0.682-0.912; P < .001), with an optimal cutoff value of 626.7. The SII may represent a practical and easily accessible biomarker for identifying patients at risk of developing CTEPH during follow-up after the first episode of unprovoked acute PE.