Relationship Between Urinary Ammonia Excretion, CKD Progression, and Survival Times in Cats with Kidney Disease

Abstract:

Background: Inadequate renal ammonia excretion drives metabolic acidosis in humans with chronic kidney disease (CKD) and is associated with poor outcomes. Data regarding its prognostic value in cats with CKD are limited. Hypothesis/

Objectives: To determine if the urine ammonia-to-creatinine ratio (UACR) is associated with disease progression and survival times in cats with CKD. Animals: 52 client-owned cats with stable IRIS Stage 1–4 CKD

Methods: Prospective longitudinal study. Clinicopathologic variables were measured at enrollment and predetermined intervals for 12 months or until death. Progression was defined as >25% increase in serum creatinine. Survival and progression were analyzed using Kaplan-Meier, log-rank tests, and Cox proportional hazards regression.

Results: Median enrollment UACR was 4.5 (range, 0.2–11.4). Cats that died had significantly lower enrollment UACR (median 2.7) than survivors (median 5.6; P=0.0006). UACR < 4.6 strongly predicted mortality (AUC 0.8571, P< 0.001) and was associated with shorter median survival (298 days) compared to UACR ≥4.6 (median not reached; P=0.014). Cats with progressive CKD had significantly lower UACR (median 2.6) than cats with non-progressive CKD (median 6.2; P< 0.0001). Median time to progression was shorter for UACR < 4.6 (197 days) than UACR ≥4.6 (not reached; P< 0.001). In a multivariate Cox model, UACR < 4.6 was independently associated with increased mortality risk (Estimate = 3.685; 95% CI, 1.57–25.52). Conclusion and Clinical Importance: Reduced urinary ammonia excretion (UACR < 4.6) is associated with faster CKD progression and increased mortality in cats and may serve as a biomarker to identify cats at risk for rapid progression and guide alkali therapy.