Impact of diabetes mellitus and renal insufficiency on 5-year mortality following coronary artery bypass graft surgery: a cohort study of 4869 UK patients

OBJECTIVES: Diabetes mellitus (DM) and renal impairment (RI) are both independent predictors of mortality after coronary artery bypass graft surgery (CABG). The two conditions often coexist, yet the impact on long-term prognosis after CABG of each factor relative to the other and the two in combination is uncertain. METHODS: We undertook a prospective cohort study of 4869 patients who underwent CABG between 2003 and 2007. The cohort was divided into four groups according to preoperative diabetic status and renal function: patients without either DM or RI (reference group), patients with DM alone, patients with RI alone and patients with both DM and RI. Clinical outcomes were compared between groups. Patients receiving renal replacement therapy were excluded. The primary outcome was 5-year all-cause mortality. RESULTS: The crude 5-year all-cause mortality rate was 9.0% for patients in the reference group, 11.1% for patients with DM alone, 20.3% for patients with RI alone and 28.5% for patients with both DM and RI (P< 0.0001). Five-year survival adjusted for potential confounding factors was significantly worse for patients with DM (hazard ratio (HR) 1.30; 95% confidence interval (CI) 1.06–1.59), patients with RI (HR 1.32; 95% CI 1.08–1.61) and patients with both DM and RI (HR 2.04; 95% CI 1.65–2.53) when compared with patients with neither condition. CONCLUSIONS: Preoperative DM and RI were important predictors of 5-year mortality after CABG. Patients with RI alone had a higher mortality rate than patients with DM alone, but this difference was largely accounted for by age and other comorbidities. The combination of DM and RI doubled the 5-year mortality rate after CABG independently of potential confounding factors.