Relationship between Peripheral Blood Inflammatory Factors and Prognosis of Subarachnoid Hemorrhage: A Meta-Analysis

Introduction: Subarachnoid hemorrhage (SAH) is a severe cerebrovascular event with high mortality and disability rate. Neuroinflammation is involved in the brain injury after SAH, but the exact association between SAH progression and peripheral blood inflammatory factors is unknown. Therefore, to determine the relationship between inflammatory factors and the prognosis of SAH, we performed a meta-analysis. Method: A systematic literature review was conducted in PubMed, Embase, and the Cochrane Library. Studies comparing the relationship between inflammatory factors (C-reactive protein [CRP], interleukin-6 [IL-6], interleukin-10 [IL-10], and tumor necrosis factor [TNF-α]) and prognosis of SAH were included in the study. A random-effects meta-analysis was conducted based on mRS, GOS, and the occurrence of cerebral vasospasm, delayed cerebral ischemia, and delayed ischemic neurologic deficits. Sensitivity analysis was performed using the leave-one-out method. The Newcastle-Ottawa Scale (NOS) for case-control studies was used to assess the quality of included studies. For continuous variables, we calculated the mean difference with a 95% confidence interval (CI). Results: 1,469 patients from 18 case-control studies met the inclusion criteria. The results found that patients in the good outcome group had significantly lower CRP levels than those in the poor outcome group (SMD: −1.15, 95% CI: −1.64 to −0.66, p < 0.00001, I2 = 87%), and peripheral IL-6 levels were significantly lower in SAH patients with the good functional outcome than those with the poor functional outcome (SMD: −0.99, 95% CI: −1.48 to −0.51, p < 0.0001, I2 = 88%). As for IL-10 (SMD: −0.28, 95% CI: −0.97 to 0.42, p = 0.43, I2 = 88%) and TNF-α (SMD: −0.40, 95% CI: −0.98 to 0.19, p = 0.18, I2 = 79%), due to the small number of studies, heterogeneity, and uncontrollable factors, robust conclusions cannot be drawn. Conclusion: SAH patients with good prognoses have significantly lower peripheral CRP and IL-6 levels. In addition, due to the small number of studies, heterogeneity, and uncontrollable factors, robust conclusions cannot be drawn for IL-10 and TNF-α. More high-quality studies are needed in the future to provide more specific recommendations for the clinical practice of inflammatory factors.