Measuring serum creatinine within six hours after cardiac surgery may improve clinicians’ ability to predict development of acute kidney injury (AKI), researchers found.

After cardiac surgery, AKI confers substantial long-term risk of death and chronic kidney disease, they noted.

The study, led by Claudio Rigatto, MD, of the University of Manitoba in Winnipeg, Canada, included 350 patients undergoing elective cardiac surgery (valve or coronary artery bypass grafting) requiring cardiopulmonary bypass. After surgery, 176 patients (52%) had a serum creatinine decrease greater than 10% compared with baseline, 26 (7.4%) had an increase greater than 10%, and 143 had a serum creatinine level less than 10% above or below baseline values. These patients served as the reference group for the study. The researchers predicted the risk of developing postoperative AKI using criteria from a base model (bypass pump time, baseline estimated glomerular filtration rate, and European System for Cardiac Operative Risk Evaluation) with and without the use of serum creatinine changes immediately (within six hours) after surgery.

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AKI developed in 53 (14%) of the 350 patients in the study. The researchers defined AKI using criteria established by the Kidney Disease: Improving Global Outcomes (KDIGO) program of the National Kidney Foundation. AKI is defined as an increase in serum creatinine level greater than 0.3 mg/dL within 48 hours or an increase greater than 1.5 times baseline within one week.

The C statistic was 0.69 for the base model alone compared with 0.78 for the base model plus the change from baseline in serum creatinine values immediately after surgery. The difference represents a statistically significant improvement in predictive value with the use of serum creatinine.

When added to the base model, a 10% or greater decrease in serum creatinine from baseline predicted a significant 63% decreased AKI risk compared with reference values, according to a report in the American Journal of Kidney Diseases. A 10% or greater increase was associated with a significant 6.4 times increased risk of AKI.

The authors noted that serum creatinine level has many known shortcomings as a marker of renal injury and glomerular filtration rate, but it remains the standard for diagnosing AKI because it is inexpensive to determine and readily available.

“Our study has potential implications for the evaluation of novel biomarkers in other studies of postsurgical AKI,” the researchers wrote. “The performance of a novel biomarker should always be evaluated in comparison to the ‘best’ base model composed of already established and readily available clinical and biochemical biomarkers.”