Fractional excretion of electrolytes in volume-responsive and intrinsic acute kidney injury in dogs: Diagnostic and prognostic implications

Background: The value of fractional excretion (FE) of electrolytes to characterize and prognosticate acute kidney injury (AKI) is poorly documented in dogs. Objectives: To evaluate the diagnostic and prognostic roles of FE of electrolytes in dogs with AKI. Animals: Dogs (n=135) with AKI treated with standard care (February 2014-December 2016). Methods: Prospective study. Clinical and laboratory variables including FE of electrolytes, were measured upon admission. Dogs were graded according to the AKI-IRIS guidelines and grouped according to AKI features (volume-responsive, VR-AKI; intrinsic, I-AKI) and outcome (survivors/non-survivors). Group comparison and regression analyses with hazard ratios (HR) evaluation for I-AKI and mortality were performed. P<.05 was considered significant. Results: Fifty-two of 135 (39%) dogs had VR-AKI, 69/135 (51%) I-AKI and 14/135 (10%) were unclassified. I-AKI dogs had significantly higher FE of electrolytes, for example, FE of sodium (FENa, %) 2.39 (range 0.04-75.81) than VR-AKI ones 0.24 (range 0.01-2.21; P<.001). Overall, case fatality was 41% (55/135). Increased FE of electrolytes were detected in nonsurvivors, for example, FENa 1.60 (range 0.03-75.81) compared with survivors 0.60 (range 0.01-50.45; P=.004). Several risk factors for death were identified, including AKI-IRIS grade (HR=1.39, P=.002), FE of electrolytes, for example, FENa (HR=1.03, P<.001), and urinary output (HR=5.06, P<.001). Conclusions and Clinical Importance: Fractional excretion of electrolytes performed well in the early differentiation between VR-AKI and I-AKI, were related to outcome, and could be useful tools to manage AKI dogs in clinical practice.