Preoperative anemia as a marker of postoperative outcomes: a retrospective cohort study

Abstract

Background: Preoperative anemia is common and associated with adverse postoperative outcomes. Objective: To evaluate the association between preoperative anemia severity and clinical outcomes in patients undergoing elective noncardiac surgery. Methods: This retrospective cohort included 23,579 adults assessed preoperatively between January 2015 and August 2025, all with documented hemoglobin (Hb) and hospitalized for noncardiac surgery. Patients were stratified as no anemia (≥ 13 g.dL−1), mild (11.1‒12.9 g.dL−1), moderate (8.1‒11.0 g.dL−1), or severe anemia (≤ 8.0 g.dL−1). Outcomes were in-hospital mortality, Intensive Care Unit (ICU) admission, and Length of Stay (LOS). Analyses used Poisson regression with robust variance adjusted for confounders. Results: Among the participants, 15,909 (67.5%) had no anemia, 6,396 (27.1%) mild, 1,174 (5.0%) moderate, and 100 (0.4%) severe anemia. Overall, 62.6% were female, and the mean age was 60.7 years (SD ±15.4). Compared with no anemia, all anemia categories were independently associated with higher in-hospital mortality, increased ICU admission, and longer LOS. Severe anemia was the strongest predictor of in-hospital mortality (adjusted RR = 24.7; 95% CI 13.3‒46.0; p < 0.001). Intermediate or major surgeries (RR = 4.7; 95% CI 3.4‒6.6), age > 54 years (RR = 4.4; 95% CI 2.6‒7.6), and male sex (RR = 2.1; 95% CI 1.6‒2.9) were also independent predictors of in-hospital mortality. Conclusions: Preoperative anemia, even when mild, was independently associated with higher in-hospital mortality, greater ICU admission, and prolonged hospitalization. These results support systematic screening and targeted management, including Patient Blood Management (PBM) strategies, to improve perioperative outcomes.