Postoperative Change in Serum Creatinine Helps Predict AKI Risk

Measuring the change in serum creatinine immediately after cardiac surgery may help in predicting acute kidney injury (AKI), suggests a study in the American Journal of Kidney Diseases.

The prospective study included 350 patients undergoing elective coronary artery bypass grafting or valve replacement surgery in Winnipeg, Canada, from 2007 to 2009. Serum creatinine was measured at baseline and within 6 hours after the end of surgery, and then each day during the remaining hospital stay. The immediate postoperative change in serum creatinine (ΔSCr) was evaluated as a predictor of AKI, based on Kidney Disease: Improving Global Outcomes (KDIGO) criteria.

The ΔSCr was decreased by more than 10 percent of baseline in 52 percent of patients. Fourteen percent met the KDIGO criteria for AKI during their hospitalization. The factors associated with AKI in a base model were bypass pump time, baseline estimated GFR, and European System for Cardiac Risk Evaluation score.

The ΔSCr was strongly associated with the development of AKI. The c statistic, an indicator of discrimination, increased from 0.69 in the base model to 0.78 after the addition of ΔSCr. The risk of AKI was more than six times higher (odds ratio 6.38) for patients with a 10 percent or greater reduction in serum creatinine. In contrast, AKI was significantly reduced (odds ratio 0.37) for those with a 10 percent or greater increase in serum creatinine.

New approaches are needed to identify patients at increased risk of AKI after cardiac surgery. Recent studies suggest that changes in creatinine before and after surgery may have better predictive ability than single baseline measurements.

Patients with an increase of more than 10 percent in serum creatinine measured within 6 hours after elective cardiac surgery are at high risk of AKI, the new study suggests. A model including the ΔSCr shows increased predictive ability. The authors note that their study used a surrogate marker of AKI, rather than clinical events [Ho J, et al. Serum creatinine measurement immediately after cardiac surgery and prediction of acute kidney injury. Am J Kidney Dis 2012; 59:196–201].

March 2012 (Vol. 4, Number 3)