BACKGROUNDAlthough low preoperative haemoglobin (Hb) concentration is a well known risk factor for adverse outcome, little is known about decreases in Hb and postoperative Hb concentrations.OBJECTIVESThe aim of this study was to evaluate the prognostic impact of both pre- and postoperative Hb concentrations (divided into low, intermediate and high tertiles) as well as Hb decrease, defined as preoperative minus postoperative Hb (gdl(-1)), on postoperative cardiovascular events in vascular surgery patients.DESIGNA retrospective observational cohort study.SETTINGErasmus University Medical Centre, Rotterdam, the Netherlands, from 1 January 2002 to 31 December 2011.PATIENTSOne thousand four hundred and eighty-four patients underwent elective open or endovascular abdominal aortic repair (aneurysm or stenosis), lower extremity arterial repair or carotid surgery. Patients for whom pre or postoperative Hb concentrations were not available were excluded.MAIN OUTCOME MEASURESThe study endpoint was 30-day postoperative cardiovascular events, including myocardial infarction, heart failure, arrhythmias, stroke, asymptomatic troponin-T release and cardiovascular death.RESULTSIn 1041 patients, both pre and postoperative Hb concentrations were available. Thirty-day cardiovascular events occurred in 221 (21%) patients. Multivariable logistic regression analyses, adjusting for age, sex, Revised Cardiac Risk Index (high-risk surgery, coronary heart disease, heart failure, cerebrovascular disease, diabetes mellitus, renal insufficiency), hypertension and hypercholesterolaemia, demonstrated that low preoperative Hb (8.7 to 12.9gdl(-1)) was associated with 30-day events [odds ratio (OR) 1.7; 95% confidence interval (CI) 1.1 to 2.5]. Intermediate (10.6 to 12.1gdl(-1)) and low (7.4 to 10.5gdl(-1)) postoperative Hb and Hb decrease were also associated with an independently increased risk of 30-day events (intermediate Hb: OR 1.7; 95% CI 1.1 to 2.7; low Hb: OR 3.1; 95% CI 2.0 to 4.8; and Hb decrease: OR 1.2; 95% CI 1.1 to 1.3, respectively). Sensitivity analyses excluding patients with transfusions (n=314) demonstrated that only postoperative Hb concentrations remained associated with a high risk of 30-day cardiovascular events (intermediate Hb: OR 1.8; 95% CI 1.0 to 3.3 and low Hb: OR 2.0; 95% CI 1.0 to 4.0).CONCLUSIONPre and postoperative Hb concentrations and Hb decrease are all related to 30-day cardiovascular events in elective vascular surgery patients. Postoperative Hb concentrations are the strongest predictor of 30-day cardiovascular events.