Urinary biomarkers in the early diagnosis of acute kidney injury

A change in the serum creatinine is not sensitive for an early diagnosis of acute kidney injury. We evaluated urinary levels of matrix metalloproteinase-9 (MMP-9), N-acetyl-β-D-glucosaminidase (NAG), and kidney injury molecule-1 (KIM-1) as biomarkers for the detection of acute kidney injury. Urine samples were collected from 44 patients with various acute and chronic kidney diseases, and from 30 normal subjects in a cross-sectional study. A case–control study of children undergoing cardio-pulmonary bypass surgery included urine specimens from each of 20 patients without and with acute kidney injury. Injury was defined as a greater than 50% increase in the serum creatinine within the first 48 h after surgery. The biomarkers were normalized to the urinary creatinine concentration at 12, 24, and 36 h after surgery with the areas under the receiver-operating characteristic curve compared for performance. In the cross-sectional study, the area under the curve for MMP-9 was least sensitive followed by KIM-1 and NAG. Combining all three biomarkers achieved a perfect score diagnosing acute kidney injury. In the case–control study, KIM-1 was better than NAG at all time points, but combining both was no better than KIM-1 alone. Urinary MMP-9 was not a sensitive marker in the case–control study. Our results suggest that urinary biomarkers allow diagnosis of acute kidney injury earlier than a rise in serum creatinine.