Hemoglobin Level Adversely Impacts Stroke Mortality

red blood cells
red blood cells
Associations with increased mortality were found for both low and high hemoglobin levels, suggesting a U-shaped relationship.

Patients with a low hemoglobin count may have a greater risk of mortality after stroke compared to non-anemic patients, new data suggest.

The study, published in the Journal of the American Heart Association, is the latest to provide strong evidence in support of the association between anemia and poor stroke outcomes.

While anemia is common in patients with acute stroke, previous research has produced conflicting evidence of its relationship to stroke mortality. Some data, for instance, suggests that both low and high levels of hemoglobin contribute to increased stroke mortality, suggesting that there is a U-shaped relationship between the 2 factors.

In order to better understand how hemoglobin levels affect stroke outcomes, Phyo K. Myint, MD, professor of medicine of old age at the University of Aberdeen in Scotland, and colleagues analyzed data from 8013 stroke patients (mean age: 77 years; 52.4% female) admitted to UK hospitals over 11 years. The effect of anemia on stroke mortality was measured at 7 days, 14 days; 1,3, and 6 months; and 1 year after stroke.

Nearly 25% of patients presenting with acute stroke had anemia, and in turn an increased comorbidity burden. Generally, anemia was associated with greater odds of mortality up to 1 year following either ischemic or hemorrhagic stroke, although the association was weaker in men with hemorrhagic stroke. Notably, elevated hemoglobin levels were also found to be associated with an increased risk of death, especially within the first month after stroke.

Additionally, women with anemia and positive vascular indication were less likely to be receiving treatment with antithrombotics compared to patients without anemia (P=.032). The opposite was observed in men; those with a negative vascular indication and anemia were more likely to be receiving antithrombotics than those without anemia (P<.001). 

To further elucidate the association between anemia and stroke mortality, the study authors conducted a systematic review and meta-analysis of 20 studies that looked at the impact of anemia on stroke and the association between hemoglobin levels and stroke. Ultimately, the total pooled study population when combined with the current study was 29,943 individuals.

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Meta-analyses showed that anemia is associated with increased stroke mortality in ischemic stroke (pooled OR: 1.97; 95% CI 1.57–2.47), as well as a less significant association in hemorrhagic stroke (OR: 1.46; 95% 1.23–1.74). “Although available data suggest that elevated hemoglobin predicts short-term mortality in ischemic stroke, findings are less consistent for hemorrhagic stroke,” the authors wrote.

The authors identified several pathological reasons for the association between anemia and stroke mortality, including intensified ischemia and hypoxia in penumbral lesions due to reduced oxygen-capacity in the blood, as well as fluctuations in cerebral perfusion. They also noted a clinical inconsistency in the prescribing of antithrombotics in anemic women vs men, “supporting previous observations that inappropriate prescribing may be more prevalent for women,” they wrote.

Unfortunately, the scarcity of evidence surrounding the association leaves many questions regarding intervention targets, including the benefit of transfusions and optimal hemoglobin range in patients with acute stroke.

“One example of an intervention might be treating the underlying causes of anemia, such as iron deficiency, which is common in this age group,” Raphae Barlas, co-author and medical student at the University of Aberdeen, suggested in a statement. “As the study has convincingly demonstrated, anemia does worsen the outcome of stroke, so it is very important that we identify at-risk patients and optimize the management.”

Disclosures: The study was funded by the Norfolk and Norwich University Hospital (NNUH) NHS Foundation Trust Stroke Services and NNUH Research and Development Department. Dr Myint reported a one-time honorarium from ViForPharma for his role as an advisory panel member.


Barlas R, Honney K, Loke Y, et al. Impact of hemoglobin levels and anemia on mortality in acute stroke: analysis of UK regional registry data, systematic review, and Meta‐AnalysisJ Am Heart Assoc. 2016;5(8):e003019. doi:10.1161/jaha.115.003019.