BackgroundThe value of fractional excretion (FE) of electrolytes to characterize and prognosticate acute kidney injury (AKI) is poorly documented in dogs.ObjectivesTo evaluate the diagnostic and prognostic roles of FE of electrolytes in dogs with AKI.AnimalsDogs (n = 135) with AKI treated with standard care (February 2014‐December 2016).MethodsProspective 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.ResultsFifty‐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 ImportanceFractional 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.

Background: Urine neutrophil gelatinase-associated lipocalin (NGAL) is a promising biomarker of acute kidney injury (AKI) in dogs.Objectives: To evaluate the utility of urinary NGAL for characterizing AKI according to volume responsiveness, presence of inflammation and sepsis, and prognosis.Animals: Dogs with AKI (n = 76) and healthy controls (n = 10).Methods: Prospective study. Clinical and clinicopathologic data including absolute urine NGAL concentration (uNGAL) and NGAL normalized to urine creatinine concentration (uNGALC) were measured upon admission. Dogs were graded according to International Renal Interest Society (IRIS) AKI guidelines and compared based on AKI features: volume-responsive (VR-) AKI vs. intrinsic (I-) AKI based on IRIS criteria; VR-AKI and I-AKI based on urine chemistry; inflammatory versus noninflammatory; septic versus nonseptic; and survivors versus nonsurvivors. Nonparametric statistics were calculated, and significance set at P < .05.Results: Urinary NGAL was significantly higher in dogs with AKI compared to controls, regardless of AKI grade. Urinary NGAL did not differ between dogs with VR-AKI and I-AKI based on IRIS criteria, whereas higher uNGALC was recorded in dogs with I-AKI based on urine chemistry. Urinary NGAL was significantly higher in dogs with inflammatory AKI, whereas no difference with respect to sepsis or outcome was identified.Conclusions and Clinical Importance: Urinary NGAL is a sensitive marker for AKI in dogs, but its specificity is affected by systemic inflammation. Increased urinary NGAL in both I-AKI and VR-AKI also suggests the presence of tubular damage in transient AKI.Combining urine chemistry data with IRIS criteria could facilitate AKI characterization in dogs. K E Y W O R D Sintrinsic AKI, systemic inflammation, tubular damage, urine chemistry, volume-responsive AKI Abbreviations: AKI, acute kidney injury; CKD, chronic kidney disease; FENa, fractional excretion of sodium; I-AKI, intrinsic acute kidney injury; ICU, intensive care unit; IRIS, International Renal Interest Society; MAT, microagglutination test; NGAL, neutrophil gelatinase-associated lipocalin; sCr, serum creatinine concentration; sCRP, serum C-reactive protein concentration; uCr, urine creatinine concentration; uCr/sCr, urine creatinine to serum creatinine ratio; uNa, urine sodium concentration; uNGAL, urine neutrophil gelatinase-associated lipocalin concentration; uNGALC, urine neutrophil gelatinase-associated lipocalin to urine creatinine ratio; UO, urinary output; VR-AKI, volume-responsive acute kidney injury; VUH, veterinary university hospital; WBC, white blood cell.

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