Clinical significance of tubular and podocyte biomarkers in acute kidney injury

Abstract

Background: Acute kidney injury (AKI) is a common complication in critically ill patients. Urinary excretion of liver-type fatty acid-binding protein (L-FABP), which is expressed in the proximal tubules, reflects the presence of tubular injury. Urinary excretion of podocalyxin (PCX), a glycoprotein prominently expressed on podocytes, is associated with podocyte injury. Our aims were to evaluate the utility of urinary L-FABP for the early detection of AKI and to examine whether podocyte injury is present in AKI patients using the biomarker of urinary PCX.

Methods: Patients admitted to the intensive care unit (ICU) were divided into the AKI group (n = 14) and non-AKI group (n = 11), according to the occurrence of AKI during hospitalization in the ICU. Changes in various biomarkers were evaluated.

Results: In the AKI group, elevation of urinary L-FABP level [maximum value of L-FABP, 199.0 (92.5-433.6) μg/g creatinine, median (25-75% interquartile range)], which reflects tubular injury (area under the curve 0.95, cut-off value 44.1 μg/g Cr), occurred between -30 and 0 h before the occurrence of AKI (i.e., the time at which serum creatinine peaked), and elevation of urinary PCX level [maximum value of PCX, 389.5 (267.0-501.0) μg/g creatinine; upper limit of reference value, 160 μg/g creatinine] occurred during the time of recovery from AKI when serum creatinine levels were decreasing between 34.0 and 72.0 h after the occurrence of AKI. Furthermore, a parameter with the primary large AUC for predicting the onset of AKI was urinary L-FABP.

Conclusions: Our study suggests that L-FABP is a useful biomarker for early detection of AKI and that podocyte injury was induced during the recovery phase of AKI.