Development and validation of a sandwich ELISA for measurement of angiotensinogen in feline urine.

A validated feline urinary angiotensinogen ELISA enables noninvasive assessment of intrarenal renin-angiotensin system activity in cats.

This study describes the development and analytical validation of a sandwich ELISA for measuring angiotensinogen (AGT) in feline urine, addressing a significant gap in veterinary nephrology diagnostics. Recombinant feline AGT and specific antibodies were commercially produced, with protein identity confirmed via tandem mass spectrometry. The assay was validated using urine from both purpose-bred (n=3) and client-owned cats (n=3) across key performance parameters. The quantifiable range was 0.74–50 ng/mL, with observed urinary AGT concentrations spanning 6.03–514.24 ng/mL in tested samples. Intra-assay coefficients of variation (CV) ranged from 8.7–18.5%, and interassay CVs from 19.4–29.0%, which are considered acceptable given the wide concentration differences expected between samples. Dilutional linearity was excellent (R²>0.98) across 2-fold serial dilutions, and spike recovery was moderate (102.7–137.7%). Crossreactivity with feline albumin and angiotensin II was minimal, supporting assay specificity. Importantly, the assay is not designed to detect subtle concentration differences due to its precision limitations. Urinary AGT is a validated noninvasive biomarker of intrarenal renin-angiotensin system (RAS) activity in humans and rodents; this ELISA now enables analogous investigations in cats. Elevated intrarenal RAS activity is implicated in hypertension, chronic kidney disease progression, and proteinuria. This tool may facilitate future research into feline renal disease pathophysiology and potential therapeutic targets involving the RAS.

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