Acute kidney injury (AKI) after cardiac surgery is associated with poor outcomes and is difficult to predict. We conducted a prospective study to evaluate whether preoperative brain natriuretic peptide (BNP) levels predict postoperative AKI among patients undergoing cardiac surgery.

The Translational Research Investigating Biomarker Endpoints in Acute Kidney Injury (TRIBE-AKI) study enrolled 1139 adults undergoing cardiac surgery at 6 hospitals from 2007 to 2009 who were selected for high AKI risk. Preoperative BNP was categorized into quintiles. AKI was common with the use of Acute Kidney Injury Network definitions; at least mild AKI was a ≥0.3-mg/dL or 50% rise in creatinine (n=407, 36%), and severe AKI was either a doubling of creatinine or the requirement of acute renal replacement therapy (n=58, 5.1%). In analyses adjusted for preoperative characteristics, preoperative BNP was a strong and independent predictor of mild and severe AKI. Compared with the lowest BNP quintile, the highest quintile had significantly higher risk of at least mild AKI (risk ratio, 1.87; 95% confidence interval, 1.40–2.49) and severe AKI (risk ratio, 3.17; 95% confidence interval, 1.06–9.48). After adjustment for clinical predictors, the addition of BNP improved the area under the curve to predict at least mild AKI (0.67–0.69; P=0.02) and severe AKI (0.73–0.75; P=0.11). Compared with clinical parameters alone, BNP modestly improved risk prediction of AKI cases into lower and higher risk (continuous net reclassification index; at least mild AKI: risk ratio, 0.183; 95% confidence interval, 0.061–0.314; severe AKI: risk ratio, 0.231; 95% confidence interval, 0.067–0.506).

Preoperative BNP level is associated with postoperative AKI in high-risk patients undergoing cardiac surgery. If confirmed in other types of patients and surgeries, preoperative BNP may be a valuable component of future efforts to improve preoperative risk stratification and discrimination among surgical candidates.

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00774137.