Hemoglobin in large vessel occlusion: Look further than collaterals

•Generally, anemia is linked to poorer outcomes in ischemic stroke.•The impact of hemoglobin on brain physiology during stroke is poorly understood.•Hemoglobin was not significantly associated with collaterals in this clinical context. Abnormal hemoglobin (Hb) levels lead to poorer outcomes in ischemic stroke, though the mechanisms remain elusive. We aimed to study the role of Hb on imaging and clinical outcomes, namely on collaterals as it is a known mediator of infarct growth. Retrospective cohort study of patients with large vessel occlusion ischemic stroke admitted to our center. Demographics, clinical and imaging variables were collected, particularly baseline hemoglobin, presence of anemia and collateral score. Collaterals were scored from 0 to 3 and defined as poor if 0–1. Multivariable analyses were performed for collateral score and clinical outcomes (3-month mortality and good prognosis). We included 811 patients, 215 (26.5 %) with anemia. Patients with anemia were older, had more comorbidities and more severe strokes. Hemoglobin levels and anemia were not associated with collateral score (OR 0.97, 95 % CI 0.89–1.05, p = 0.414 and OR 0.89, 95 % CI 0.64–1.24, p = 0.487, respectively) nor with poor collaterals (OR 0.96, 95 % CI 0.88–1.05, p = 0.398 and OR 0.86, 95 % CI 0.60–1.23, p = 0.406, respectively). Hb levels were associated with 3-month mortality (OR 0.85, 95 % CI 0.76–0.96, p = 0.008). Hemoglobin or anemia were not found to be associated with collateral status. Our results raise further questions regarding the pathophysiology of anemia and outcomes in ischemic stroke, highlighting the need for future research.