Urinary angiotensinogen indexed to creatinine or protein is higher in cats with surgically induced chronic kidney disease compared to healthy cats

Objective: To compare urinary angiotensinogen, a proposed biomarker for intrarenal renin-angiotensinogen system (RAS) activity, between cats with surgically induced chronic kidney disease (CKD) and healthy cats and explore its correlation with select clinical and circulating renin-angiotensin-aldosterone system (RAAS) markers. Methods: Urine was banked from September 2022 through April 2023 during a study comparing circulating RAAS markers between cats with induced CKD and sex- and life stage-matched healthy cats. Urinary angiotensinogen concentration was measured from October 2025 through July 2026 using a validated in-house ELISA. Urinary concentration of angiotensinogen was indexed to that of creatinine or protein to account for urine concentration or indiscriminate urinary protein loss, respectively. Results: 28 cats (n = 14/group) were included. The median (IQR) indexed urinary angiotensinogen was higher in cats with CKD than in healthy cats (urinary angiotensinogen-to-protein ratio, 9.80 [5.47, 17.22] vs 3.38 [1.09, 5.52]; urinary angiotensinogen-to-creatinine ratio, 0.99 [0.40, 2.34] vs 0.31 [0.21, 0.60]). In cats with CKD, indexed urinary angiotensinogen correlated positively with serum creatinine concentration (urinary angiotensinogen-to-protein ratio, ρ = 0.573; urine angiotensinogen-to-creatinine ratio, ρ = 0.642). In healthy cats, urinary angiotensinogen-to-creatinine ratio correlated negatively with several circulating RAAS markers, including serum angiotensin II (ρ = -0.547) and angiotensin 1-7 (ρ = -0.631) equilibrium concentrations. Conclusions: The intrarenal RAS, assessed by urinary angiotensinogen, is activated in cats with induced CKD, and its activity is inversely related to that of the circulating RAAS in healthy cats but not those with CKD. Clinical Relevance: Concurrent evaluation of circulating RAAS and intrarenal RAS markers is required for complete assessment of this system.