Presurgical Serum Cystatin C and Risk of Acute Kidney Injury After Cardiac Surgery

Background Acute kidney injury (AKI) after cardiac surgery is associated with poor outcomes, but is challenging to predict from information available before surgery. Study Design Prospective cohort study. Setting & Participants The TRIBE-AKI (Translational Research Investigating Biomarker Endpoints in Acute Kidney Injury) Consortium enrolled 1,147 adults undergoing cardiac surgery at 6 hospitals from 2007-2009; participants were selected for high AKI risk. Predictors Presurgical values for 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. Outcomes The primary outcome was AKI Network (AKIN) stage 1 or higher; ≥0.3 mg/dL or 50% increase in creatinine level. Measurements Analyses were adjusted for characteristics used clinically for presurgical risk stratification. Results Average age was 71 ± 10 years (mean ± standard deviation); serum creatinine, 1.1 ± 0.3 mg/dL; eGFR-Cr, 74 ± 9 mL/min/1.73 m2 ; and cystatin C, 0.9 ± 0.3 mg/L. 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 with creatinine, based on a net reclassification index of 0.21 ( P < 0.001). Limitations The ability of these kidney biomarkers to predict risk of dialysis-requiring AKI or death could not be assessed reliably in our study because of a small number of patients with either outcome. Conclusions Presurgical cystatin C is better than creatinine or creatinine-based eGFR at forecasting the risk of AKI after cardiac surgery.