Correlation of Urine Ammonia Excretion With Renal Function in Healthy Cats and Cats With Kidney Disease.

BACKGROUND: Inadequate ammonia excretion is thought to drive the development of metabolic acidosis in people with CKD and to correlate with worse outcomes. OBJECTIVES: To determine if urine ammonia-to-creatinine ratio (UACR) correlates with serum creatinine as a renal function marker in healthy cats and cats with CKD and whether UACR is related to the presence of CKD. ANIMALS: The study group comprised 74 healthy and 45 stable IRIS stage 2-4 CKD cats. METHODS: 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 using the Mann-Whitney test. Correlation between UACR concentrations and serum renal and electrolyte values used Spearman's correlation test. Relationships between UACR, renal variables, electrolytes, urine specific gravity, age, and body weight were explored with multiple linear regression. RESULTS: Chronic kidney disease cats (median 4.2; range 0.6-9.2) had lower UACR than healthy cats (median 7.6; range 3.0-23.7; p < 0.01). UACR was inversely correlated with creatinine concentration (p < 0.01, r(s) = -0.545). 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 with declining renal function.