Urinary cystatin C levels as a diagnostic and prognostic biomarker in patients with acute kidney injury

Aim Acute kidney injury ( AKI ) is a frequent complication in critically ill patients and is associated with a high mortality. Clinicians have limited tools to predict the course of AKI at the time of serum creatinine increase. We evaluated the diagnostic and prognostic utility of urinary cystatin C ( uCysC ) in patients with AKI . Methods In this study, serum and uCysC and urinary creatinine (uCr) were measured in patients presenting with acute kidney injury. The patients were divided into two groups: those with prerenal AKI and those with an intrinsic AKI . Prerenal AKI was defined as a new‐onset increase in serum creatinine (sCr) that resolved within 72 h and returned to the baseline kidney function level. Patients with intrinsic AKI were defined and classified according to the A cute K idney I njury N etwork ( AKIN ) criteria. Results Of the total number of patients ( n  = 213), 40.4% ( n  = 86) were judged to have prerenal AKI and 59.6% ( n  = 127) intrinsic AKI . uCysC values and the uCysC/uCr ratio were significantly higher in intrinsic AKI   versus prerenal AKI . In intrinsic AKI , the uCysC concentration increased with AKI severity. The uCysC/uCr ratio was significantly higher in the RRT group versus the non‐ RRT group (0.15 vs . 0.08, respectively; P  = 0.037). In a multivariate analysis, the uCysC/uCr ratio was associated with in‐hospital mortality ( P  = 0.019). Conclusions uCysC level and the uCysC/uCr ratio were useful biomarkers of intrinsic AKI , and the uCysC/uCr ratio was predictive of in‐hospital death in AKI patients.