Comparison between three different equations for the estimation of glomerular filtration rate in predicting mortality after coronary artery bypass.

Background: This study was undertaken to compare the accuracy of chronic kidney disease-epidemiology collaboration (eGFR) to modification of diet in renal disease (eGFR) and the Cockcroft-Gault formulas of Creatinine clearance (C) equations in predicting post coronary artery bypass grafting (CABG) mortality.

Methods: Data from 4408 patients who underwent isolated CABG over a 11-year period were retrieved from one institutional database. Discriminatory power was assessed using the c-index and comparison between the scores' performance was performed with DeLong, bootstrap, and Venkatraman methods. Calibration was evaluated with calibration curves and associated statistics.

Results: The discriminatory power was higher in eGFR than eGFR and C (Area under Curve [AUC]:0.77, 0.55 and 0.52, respectively). Furthermore, eGFR performed worse in patients with an eGFR ≤29 ml/min/1.73m (AUC: 0.53) while it was not influenced by higher eGFRs, age, and body size. In contrast, the MDRD equation was accurate only in women (calibration statistics p = 0.72), elderly patients (p = 0.53) and subjects with severe impairment of renal function (p = 0.06) whereas C was not significantly biased only in patients between 40 and 59 years (p = 0.6) and with eGFR 45-59 ml/min/1.73m (p = 0.32) or ≥ 60 ml/min/1.73m (p = 0.48).

Conclusions: In general, CKD-EPI gives the best prediction of death after CABG with unsatisfactory accuracy and calibration only in patients with severe kidney disease. In contrast, the CG and MDRD equations were inaccurate in a clinically significant proportion of patients.