Hemoglobin and long-term risk of death in patients with acute myocardial infarction

Background Anemia is a common finding among patients with acute myocardial infarction (MI) and may be associated with worse short-term outcomes. However, contemporary data and data on long-term outcomes are lacking. Purpose To assess the association between hemoglobin (hgb) at hospitalization and risk of short- and long-term death in persons with acute MI. Methods We used the Danish registries to identify patients with a first MI diagnosis (ICD-10 diagnostic code: I21) during 2013-2020. Those who had ≥1 hgb measurement ≤24 hours of index hospitalization were included. Hgb concentrations were reported in mmol/l (conversion: 1 mmol/l = 1.61 g/dl). The association between the first measured hgb concentration and death from any cause was examined in both continuous and categorical (deciles, predefined thresholds) fashions. Absolute and relative risks for death from any cause at days 0-30 and 31-365 were calculated through multivariable Cox regression with average treatment effect modeling. Models were standardized for demographic and clinical features, including prior cardiovascular, inflammatory, or malignant disease, recent bleeding, infection, or surgical procedure, C-reactive protein and high-sensitivity troponin concentrations, and estimated glomerular filtration rate. Results A total of 32,928 individuals were included. Median age was 69.4 (interquartile range [IQR]: 58.6-78.5) years, and 34.5% were women. Median hgb concentration was 8.5 (IQR: 7.8-9.2) mmol/l. Hgb was significantly and nonlinearly associated with death (p<0.001) (Figures). At 0-30 days, 1999 (6.1%) patients had died, and an additional 2240 (7.2%) died between days 31-365. The standardized absolute risks of death from any cause at 0-30 and 31-365 days were highest in patients in the first decile (i.e., hgb concentration <6.9 mmol/l, n=3209): 10.4% at 30 days and 12.5% at 31-365 days. The standardized risks were lowest in individuals with a hgb concentration 9.1-9.3 mmol/l, n=3325: 4.3% at 30 days and 3.9% at 31-365 days. The risk of death in the first decile was significantly higher than all other groups combined (standardized relative risk at 30 days: 1.91, 95% confidence interval [CI], 1.73 to 2.09, p<0.001; 31-365 days: 1.56, 95% CI, 1.45 to 1.66, p<0.001). The standardized risk of death was also higher in individuals with hgb concentrations below traditional transfusion thresholds, i.e., 4.3 mmol/l, 5.0 mmol/l, 5.6 mmol/l, and 6.2 mmol/l. Findings were consistent when selectively considering individuals undergoing percutaneous coronary intervention or coronary artery bypass grafting within 7 days (n=17,924), although the overall risk of death was substantially lower in this group. Conclusion In this large, contemporary cohort of patients with acute MI we found that low hgb concentration was significantly associated with a higher risk of both short- and long-term death. Our results suggest that a higher transfusion threshold might be beneficial in patients with MI.