How should acute kidney injury be diagnosed and managed in dogs and cats?

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Acute kidney injury (AKI) in dogs and cats is diagnosed by identifying acute renal parenchymal injury with or without azotemia, and managed through cause elimination, fluid optimization, complication control, and renal replacement therapy when conventional management fails. ---  Diagnosis AKI is defined as sudden renal parenchymal damage developing within approximately 48 hours, distinguished from chronic kidney disease (CKD) by the acuity of onset and, on ultrasound, by increased rather than decreased renal size and cortical thickness.18 During AKI, inflammation causes edema and increased cortical thickness, whereas CKD is associated with cortical thinning and reduced kidney length.8 This ultrasonographic distinction is clinically useful when historical baseline creatinine values are unavailable. The minimum diagnostic database includes serum creatinine, urea, phosphorus, electrolytes, acid-base status, urinalysis with urine specific gravity, and urine culture by cystocentesis.19 Biochemical markers of AKI — elevated creatinine, elevated urea, and proteinuria — appear 24 to 48 hours after a nephrotoxic or ischemic insult.4 A presumptive diagnosis of acute pyelonephritis (APN) as the cause of AKI is made when urine culture collected by cystocentesis is positive.912 Neutrophil gelatinase-associated lipocalin (NGAL) is an early damage biomarker that rises in urine and blood within hours of tubular injury, enabling detection of non-azotemic or International Renal Interest Society (IRIS) grade 1 AKI before creatinine increases.13 NGAL concentrations also correlate with the healing process and have been explored as a predictor of recovery.13 Serum fibroblast growth factor-23 (FGF-23) is elevated in dogs and cats with AKI. In dogs, median serum FGF-23 is 2104.0 pg/mL in AKI versus 278.5 pg/mL in controls, and in cats, 1195 pg/mL versus 138 pg/mL in controls.14 In dogs, serum FGF-23 correlates positively with serum creatinine (r = 0.67) and phosphate (r = 0.893).14 Dogs wi