Acute kidney injury (AKI) following cardiac surgery is associated with poor outcomes, but is challenging to predict from information available prior to surgery.
Prospective cohort study
Setting & Participants
The TRIBE-AKI Consortium enrolled 1,147 adults undergoing cardiac surgery at six hospitals from 2007–2009; participants were selected for high AKI risk.
Pre-surgical cystatin C, creatinine, and creatinine-based estimated glomerular filtration rate (eGFR) were categorized into quintiles and grouped as ‘Best’ (quintiles 1–2), ‘Intermediate’ (quintiles 3–4), and ‘Worst’ (quintile 5) kidney function.
The primary outcome was AKI Network (Acute Kidney Injury Network) Stage 1 or higher; ≥0.3mg/dL or 50% rise in creatinine.
Analyses were adjusted for characteristics used clinically for pre-surgical risk stratification.
The average age and kidney function were: 71±10 years (mean ± standard deviation), serum creatinine 1.1±0.3 mg/dL, eGFR-Cr, 74±9 mL/min/1.73m2, and cystatin C, 0.9 ±0.3 mg/L. A total of 407 (36%) participants developed AKI during hospitalization. Adjusted odds ratios for intermediate and worst kidney function by cystatin C were 1.9 (95% CI, 1.4–2.7) and 4.8 (95% CI, 2.9–7.7) compared with 1.2 (95% CI, 0.9–1.7) and 1.8 (95% CI, 1.2–2.6) for creatinine and 1.0 (95% CI, 0.7–1.4) and 1.7 (95% CI, 1.1–2.3) for eGFR-Cr categories, respectively. After adjustment for clinical predictors, the C statistic to predict AKI was 0.70 without kidney markers, 0.69 with creatinine, and 0.72 with cystatin C. Cystatin C also substantially improved AKI risk classification compared to creatinine, based on a net reclassification index of 0.21 (p<0.001).
The ability of these kidney biomarkers to predict risk for dialysis-requiring AKI or death could not be reliably assessed in our study due to a small number of patients with either outcome.
Pre-surgical cystatin C is better than creatinine or creatinine-based eGFR at forecasting the risk of AKI after cardiac surgery.