Urinary Calprotectin as a Marker to Distinguish Functional and Structural Acute Kidney Injury in Pediatric Population

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Background: Acute kidney injury (AKI) is a serious, common and occasionally under-recognized condition. To date, the clinical and some laboratory parameters are routinely applied to distinguish between functional and structural AKI which can be challenging in certain occasions. In the present paper, we investigate the accuracy of urinary calprotectin as a diagnostic biomarker in this dubious situation. Methods: This is a cross-sectional study among 75 children with AKI defined by Acute Kidney Injury Network (AKIN) and 20 healthy children as controls which was carried out for about six months (September 2014 to March 2015). Random urinary calprotectin concentration was assessed by ELISA in both groups within 48 hours after diagnosis. Patients with obstructive uropathy, malnutrition, renal transplantation, chronic renal failure, urinary tract infection, and malignancy were excluded. Receiver-operating characteristic (ROC) curves were drawn to determine the accuracy of urinary calprotectin to detect children with structural AKI. P value less than 0.05 was considered significant. Results: Median urinary calprotectin was 1240 ng/mL in structural AKI, 28.5 in functional, and 33 in controls. Receiver operating curve analysis revealed high levels of accuracy for measuring calprotectin in predicting structural AKI. A cutoff level of 230 ng/mL for urinary calprotectin showed high sensitivity and specificity. The urine calprotectin/creatinine ratio indicated the same accuracy as urinary calprotectin in diagnosing structural AKI. The ROC curve function was better for urine calprotectin and its ratio in comparison to fractional excretion of sodium (FENa). Conclusions: Calprotectin is a biomarker that can rapidly and easily recognize structural from functional AKI with high sensitivity and specificity in comparison to traditional most accurate diagnostic test; FENa.