Preoperative serum cystatin C combined with dipstick proteinuria predicts acute kidney injury after cardiac surgery

Background: Acute kidney injury (AKI) is common following cardiac surgery and is associated with poor outcomes. However, the detection of those preoperative patients who will develop AKI is still difficult. In this study, we compared serum cystatin C combined with dipstick proteinuria as early markers to predict AKI available before surgery. Methods: We prospectively followed 616 patients undergoing cardiac surgery and identified 179 that developed AKI, defined as an increase in serum creatinine (SCr) of ≥ 0.3 mg/dL or ≥ 50% increase in creatinine level. Preoperative values for cystatin C were categorized into quartiles. We defined proteinuria, measured with a dipstick, as mild (trace to 1+) or heavy (2 + to 4+). Univariate as well as multivariate regression was performed. Cystatin C combined with dipstick proteinuria before surgery was assessed for its' predictive value of AKI using receiver operating characteristic (ROC) curves. Results: The final cohort consisted of 616 patients aged 60.7 ± 13.2 years, and baseline SCr was 75.8 ± 26.4 μmol/L, estimated glomerular filtration rate (eGFR) 96.3 ± 29.0 mL/min/1.73 m2 and cystatin C 1.05 ± 0.33 mg/L. Patients in higher cystatin C quartiles were older (p < 0.001), more often to have heavy proteinuria (p = 0.021), hyperuricemia (p < 0.001), heart failure (p < 0.001) and recent myocardial infarction (p = 0.002). Those with heavy proteinuria were more often to have diabetes mellitus (p = 0.010), hyperuricemia (p = 0.043), worse cardiac function (p < 0.05), higher creatinine levels (p < 0.001) and lower eGFR levels (p < 0.001). In a multiple logistic regression model, preoperative heavy proteinuria [OR: 3.14, 95% confidence interval (CI): 1.26–7.77] and preoperative cystatin C quartiles (Q2:OR: 1.60, 95% CI: 0.72–3.60; Q3:OR: 1.87, 95% CI: 0.85–4.14; Q4:OR: 3.10, 95% CI: 1.37–7.02) each associated with an increased odds of AKI, independent of advanced age (OR: 1.04, 95% CI: 1.01–1.06), hypertension (OR: 1.88, 95% CI: 1.13–3.12) and combined surgery (OR: 3.47, 95% CI: 1.35–8.89). The risk for adverse outcomes such as postoperative AKI, persistent AKI, severe AKI, dialysis and mortality were highest in patients with highest quartile of cystatin C (p < 0.05, respectively) and heavy proteinuria (p < 0.05, respectively). The area under the ROC curve for preoperative cystatin C combined with proteinuria to detect AKI, persistent AKI and severe AKI were 0.695 (p < 0.001; 95% CI = 0.637–0.754), 0.753 (p < 0.001; 95% CI = 0.693–0.812) and 0.718 (p < 0.001; 95% CI = 0.642–0.795), respectively. Conclusion: These data suggest that preoperative serum cystatin C combined with dipstick proteinuria may improve prediction of AKI among patients undergoing cardiac surgery.