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

Urinary angiotensinogen is elevated in CKD cats, supporting its use as a non-invasive intrarenal RAS biomarker.

This study investigated urinary angiotensinogen (uAGT) as a biomarker for intrarenal renin-angiotensin system (RAS) activity in cats, comparing 14 cats with surgically induced chronic kidney disease (CKD) to 14 sex- and life stage-matched healthy controls. Urinary angiotensinogen was measured via a validated in-house ELISA and indexed to urinary creatinine (uAGT:Cr) or urinary protein (uAGT:Pr) to correct for urine concentration and nonspecific protein loss, respectively. Both indexed ratios were significantly higher in CKD cats compared to healthy cats (uAGT:Pr: 9.80 vs. 3.38; uAGT:Cr: 0.99 vs. 0.31), indicating intrarenal RAS activation in CKD. In CKD cats, both indexed uAGT values positively correlated with serum creatinine concentration, suggesting that intrarenal RAS activity increases with declining renal function. Interestingly, in healthy cats, uAGT:Cr correlated negatively with circulating RAAS markers including serum angiotensin II (ρ = -0.547) and angiotensin 1-7 (ρ = -0.631), implying an inverse physiological relationship between intrarenal and systemic RAS in healthy individuals—a relationship that appears disrupted in CKD. These findings support uAGT as a clinically useful, non-invasive biomarker for intrarenal RAS activity in cats with CKD. The authors emphasize that concurrent assessment of both circulating RAAS and intrarenal RAS markers is necessary for comprehensive evaluation of this complex system in feline patients.

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