Calprotectin and neutrophil gelatinase-associated lipocalin in the differentiation of pre-renal and intrinsic acute kidney injury.

BACKGROUND: Urinary calprotectin has recently been identified as a promising biomarker for the differentiation of prerenal and intrinsic acute kidney injury (AKI). The present study compares the diagnostic performance of calprotectin and neutrophil gelatinase-associated lipocalin (NGAL) in this differential diagnosis. METHODS: Urinary calprotectin and NGAL concentrations were assessed in a study population of 87 subjects including 38 cases of intrinsic AKI, 24 cases of prerenal AKI, and 25 healthy controls. Urinary tract obstruction, renal transplantation and metastatic cancer were defined as exclusion criteria. RESULTS: Mean calprotectin concentrations were significantly lower in prerenal (190.2+/-205.7 ng/ml) than in intrinsic AKI (6250.1+/-7167.2 ng/ml, p<0.001). Receiver operating characteristic (ROC) analysis provided an AUC of 0.99. Mean NGAL concentrations were significantly higher in intrinsic than in prerenal AKI as well (458.1+/-695.3 vs. 64.8+/-62.1 ng/ml, p=0.001) providing an AUC of 0.82. A combination of the present study population with the cohort of the proof of concept study led to a population of 188 subjects (58 prerenal AKI, 90 intrinsic AKI, 40 healthy controls). ROC analyses provided an AUC of 0.97 for calprotectin and 0.76 for NGAL yielding sensitivity and specificity values of 93.3% and 94.8% (calprotectin) vs. 75.3% and 72.4% (NGAL). Optimal cut-off values were 440 ng/ml (calprotectin) and 52 ng/ml (NGAL). Pyuria increased calprotectin concentrations independent of renal failure. CONCLUSION: The present study shows that both calprotectin and NGAL are able to differentiate between prerenal and intrinsic AKI after exclusion of pyuria. In the present population, calprotectin presents a higher sensitivity and specificity than NGAL.