NU01 - Feline Urine Ammonia-to-creatinine Ratio Reference Interval

Abstract: Background
Renal ammonia metabolism is critical to maintaining acid-base homeostasis. Inadequate ammonia excretion drives development of metabolic acidosis in people with chronic kidney disease (CKD) and correlates with worse clinical outcomes. Metabolic acidosis is commonly recognized in cats with CKD, but there is limited information about ammonia excretion in these patients.

Objectives
The purpose of this study was to generate a reference interval (RI) for urine ammonia-to-creatinine ratio (UACR) in a population of healthy adult cats.

Animals
92 adult, client-owned cats were assessed via history, physical examination, serum chemistry, and urinalysis, and 20 were excluded. Urine samples (n=72) were processed and stored under mineral oil at -80◦C.

Methods
Ammonia and creatinine concentrations were measured using commercially available enzymatic assays. To establish RI for UACR, 2.5% and 97.5% limits were determined using nonparametric methods. The Dixon method was used to detect and exclude outliers. The Anderson-Darling test was used to assess for normality, and statistical significance was set at P < 0.05 for all analyses.

Results
The RI for UACR was determined to be 3.4-20.7 with 90% confidence intervals of 3.0-3.7 and 16.0-23.7 for the lower and upper limits of detection respectively. General linear models did not detect significant relationships between UACR and serum bicarbonate, sex, weight, or age.

Conclusions and Clinical Importance
Having a RI for UACR for healthy cats will provide a foundation for future research to determine whether alterations in ammonia excretion are associated with specific disease states, which may provide prognostic information or influence clinical management strategies.