Sustained elevated neutrophil–lymphocyte ratio following aneurysmal subarachnoid hemorrhage is an independent predictor of poor outcome

PURPOSE: Aneurysmal subarachnoid hemorrhage (aSAH) is a subtype of stroke with significant morbidity and mortality at the time of rupture and days after. A pro-inflammatory response, in which neutrophils increase relative to lymphocytes, has been proposed to play a vital role in identifying the risk profile after rupture. This study aimed to identify whether neutrophil-to-lymphocyte ratio (NLR) is an independent predictor of outcomes, namely functional outcomes at ≥ 12 months, clinical delayed cerebral ischaemia (DCI), and hydrocephalus. METHODOLOGY: This prospective cohort study included 114 sequential patients admitted to the Royal Brisbane and Women's Hospital between 2020 and 2023 for the treatment of aSAH. Full blood counts were collected daily until day 14 post-ictus to determine the NLR. The primary outcome measure was functional outcome at ≥ 12 months, as defined by the modified Rankin Scale. The secondary outcome measures included hydrocephalus and clinical DCI, diagnosed as neurological deficits responsive to hypertensive treatment. A factorial analysis of variance (ANOVA) with post-hoc analysis was conducted for statistical analysis of the results. RESULTS: Twenty-five patients (21%) had a poor outcome at ≥ 12 months, 28 patients (24.6%) experienced clinical DCI, and 26 (22.8%) required long-term CSF diversion. Multivariate analysis revealed a significant relationship between the mean NLR between day 3 to day 12 post-ictus and the incidence of poor outcomes. There was no independent relationship between NLR and DCI or between NLR and hydrocephalus. CONCLUSION: An elevated NLR may be a surrogate marker for prolonged inflammation, highlighting the pathological role of dysregulated neuroinflammation, which can result in poor long-term functional outcomes. Further research should focus on elucidating the molecules driving pathogenic neuroinflammation after aSAH to highlight potential therapeutic targets.