Impact of cystatin C and RIFLE on renal function assessment after cardiac surgery

The lack of a consensus classification system and of a specific, sensitive, and early-stage biomarker for kidney injury frequently results in late diagnosis of acute kidney injury (AKI). The aim of the present study was to characterize the discriminatory power of cystatin C and the RIFLE and Acute Kidney Injury Network (AKIN) criteria for the assessment of renal dysfunction after cardiac surgery. A longitudinal, quantitative study was conducted in intensive care units of the Heart Institute (São Paulo, Brazil) in which 121 patients were followed for the first 72 hr after cardiac surgery. Most of the patients were male (61.2%), and the mean age was 50 years. The most frequent surgeries were valve replacement (48.8%) and myocardial revascularization (43.8%). AKI was defined as an increase of at least 50%, 0.3 mg/dl or 0.5 mg/dl in baseline serum creatinine. The percentage of participants meeting each of these criteria was 13.2%, 28.1%, and 11.6%, respectively. A progressive increase in cystatin C levels was associated with a worsening of renal function, as classified by RIFLE and AKIN (p < .05). Analysis of the receiver operating characteristic (ROC) curves showed the RIFLE and AKIN classification to have good discriminatory power for the assessment of renal function, with the performance of cystatin C being poorer (area under the curve: 0.804 and 0.794 vs. 0.719). However, combining cystatin C and RIFLE resulted in greater discriminatory power for detecting kidney injury in postoperative patients than any marker in isolation.