Urinary Calprotectin Predicts Severe Acute Kidney Injury After Non-cardiac Surgery in Surgical Intensive Care Unit: A Prospective Cohort Study

Background Postoperative risk stratification for severe acute kidney injury (AKI) can facilitate timely intervention and improve prognosis. Objectives This study aimed to evaluate the added predictive ability of urinary calprotectin for postoperative risk stratification of severe AKI in non-cardiac surgery patients. Design A total of 580 patients were enrolled, and 98 (17%) developed severe AKI with a median time of 12.8 hours after SICU admission. Methods In a prospective cohort of patients transferred to the surgical intensive care unit (SICU) after non-cardiac surgery, calprotectin was measured in urine samples collected 0, 6, and 12 hours after SICU admission. A clinical model for predicting severe AKI was established. We tested the ability of urinary calprotectin alone to predict severe AKI by area under the receiver operating characteristics curve (AUC) analysis. We further evaluated the improvement of the pre-diction ability after adding urinary calprotectin in the clinical model by the increment in AUC, relevant integrated discrimination improvement (IDI), and net reclassification improvement (NRI). Results Higher urinary calprotectin levels were observed in the severe AKI group at any time point (All P<0.001). In the entire cohort, the AUC of urinary calprotectin at SICU admission for predicting severe AKI was 0.701(95% CI, 0.649 to 0.754), and calprotectin ≥32.3 ng/ml was associated with increased risk (OR 6.119, 95% CI 3.259 – 11.488). The AUC of the clinical model increased from 0.693 (95%CI, 0.633 to 0.754) to 0.730 (95%CI, 0.677 to 0.784) upon adding urinary calprotectin, the NRI was 0.337 (P<0.001) and the IDI was 0.055 (P<0.001). Conclusion A combination of urinary calprotectin and clinical features could be useful for postoperative risk stratification of severe AKI in non-cardiac surgery patients.