Correlation of urine ammonia excretion with renal function in healthy dogs and dogs with chronic kidney disease

BACKGROUND: Inadequate ammonia excretion is thought to drive the development of metabolic acidosis in people with chronic kidney disease (CKD) and correlates with worse clinical outcomes, such as faster progression to end-stage kidney disease and increased case fatality. HYPOTHESIS/OBJECTIVES: To determine if urine ammonia-to-creatinine ratio (UACR) correlates with serum creatinine concentration as a renal function marker in healthy dogs and dogs with CKD and whether UACR is altered in the presence of CKD. ANIMALS: The study group comprised 46 healthy and 50 stable International Renal Interest Society (IRIS) Stages 2, 3, and 4 CKD dogs. METHODS: This was a prospective, single-time point study. Serum biochemistry variables were measured. Urinary ammonia and creatinine concentrations were measured and used to calculate UACR. Group comparisons were made with the Mann-Whitney test. Correlation between UACR and serum renal and electrolyte values was assessed using Spearman's correlation test. Relationships between UACR, renal variables, electrolytes, urine specific gravity, age, and body weight were explored with multiple linear regression. RESULTS: CKD dogs had lower UACR (median 2.2; range 0.9-10.5) than healthy dogs (median 7.1; range 0.7-40.0) (P < .001). UACR was inversely correlated with creatinine concentrations (P < .001, rs = -0.535). The relationship between UACR and creatinine persisted after controlling for age, body weight, electrolytes, renal functional variables, and urine specific gravity. CONCLUSIONS AND CLINICAL IMPORTANCE: These findings suggest that ammonia excretion is impaired in dogs with diminished renal function.