Background: Preoperative anemia is common in patients scheduled for cardiac surgery. However, its effect on postoperative outcomes remains controversial. This meta-analysis aimed to clarify the impact of anemia on outcomes after cardiac surgery. Methods: A literature search was conducted on MEDLINE, Embase, Cochrane, and Web of Science databases. The primary outcome was 30-day postoperative or in-hospital mortality. Secondary outcomes included acute kidney injury, stroke, blood transfusion, and infection. A meta-analytic model was used to determine the differences in the above postoperative outcomes between anemic and nonanemic patients. Results: Of 1103 studies screened, 22 met the inclusion criteria. Of 114,277 patients, 23,624 (20.6%) were anemic. Anemia was associated with increased mortality (odds ratio [OR], 2.74; 95% confidence interval [CI], 2.32-3.24; I2 = 69.6%; P < .001), acute kidney injury (OR, 3.13; 95% CI, 2.37-4.12; I2 = 71.1%; P < .001), stroke (OR, 1.46; 95% CI, 1.24-1.72; I2 = 21.6%; P < .001), and infection (OR, 2.65; 95% CI, 1.98-3.55; I2 = 46.7%; P < .001). More anemic patients were transfused than nonanemic patients (33.3% vs 11.9%, respectively). No statistically significant association was found between mortality and blood transfusion (OR, 1.35; 95% CI, 0.92-1.98; I2 = 83.7%; P = .12), but we were not able to compare mortality with or without transfusion in those who were or were not anemic. Conclusions: Preoperative anemia is associated with adverse outcomes after cardiac surgery. These findings support the addition of preoperative anemia to future risk prediction models and as a target for risk modification.
