Urinary Cystatin B as a marker of acute kidney injury in cats

Diagnosing acute kidney injury (AKI) might be challenging due to lack of sensitive early markers. The objective of this study was to evaluate the diagnostic and prognostic utility of the urinary biomarker Cystatin B (uCysB) in cats with AKI. Seventy-six client-owned cats were included. Urine samples of healthy cats and cats with various urinary tract disease including urethral obstruction (UO), chronic kidney disease (CKD) and AKI, were collected. uCysB concentration was measured using a research sandwich format ELISA at IDEXX Laboratories, Inc. uCysB was different among groups (P <0.001). uCysB was higher in the AKI (P <0.001) and CKD (P =0.006) groups compared with controls [1052 ng/mL (range, 7-3858) and 112 ng/mL (range, 14-1370) vs. 22 ng/mL (range, 11-154), respectively]. Cats with AKI had higher uCysB compared with cats with CKD (P =0.001) or UO (P =0.004). Receiver operator characteristic curve (ROC) analysis of uCysB as an AKI predictor vs. controls had an area under the curve (AUC) of 0.92 (95 % CI, 0.84-1.0). An 84 ng/mL cutoff point corresponded to sensitivity and specificity of 90 % and 92 %, respectively. uCysB concentration was higher in AKI non-survivors compared with survivors (1572 ng/mL, range, 140-3858 vs. 584 ng/mL, range, 7-2803 respectively; P =0.004). ROC analysis of uCysB as an AKI outcome predictor had an AUC of 0.84 (95 % CI, 0.56-1.0), with an optimal cut-off point of 469 ng/mL, corresponding to sensitivity and specificity of 100 % and 75 % respectively. In conclusion, uCysB is a useful diagnostic and prognostic marker of AKI in cats.