Assessment of kidney injury biomarkers in cats with obstructive and non‐obstructive lower urinary tract disease

BACKGROUND: Feline lower urinary tract disease (FLUTD) is a common and potentially life-threatening condition in cats, with obstructive and non-obstructive presentations. This study aimed to evaluate tubular injury in cats with FLUTD using serum and urinary biomarkers. METHODS: Forty male cats were enrolled and assigned to three groups: obstructive (n = 16), non-obstructive (n = 15) and healthy controls (n = 9). Urea nitrogen, creatinine, albumin and ELISA-based biomarker analyses (retinol-binding protein [RBP], N-acetyl-β-D-glucosaminidase [NAG], neutrophil gelatinase-associated lipocalin, cystatin-C [Cys-C], kidney injury molecule-1 [KIM-1] and interleukin-18 [IL-18]) were performed on serum and urine samples. The data were analysed using Kruskal‒Wallis test and Dunn's post hoc test. RESULTS: Obstructive cats exhibited significantly elevated urinary RBP, NAG, KIM-1, IL-18 and albumin concentrations and indexes of RBP, NAG, Cys-C and KIM-1. Non-obstructive cats also showed elevations in urinary RBP and KIM-1. LIMITATIONS: The small sample size and absence of histopathological or follow-up data limit interpretation, although post hoc analysis showed strong power for most biomarkers except Cys-C and NAG. CONCLUSION: Our findings suggest that both obstructive and non-obstructive FLUTD may involve mild tubular stress. Since only a single time point was evaluated, it remains unclear whether these changes are transient or persistent. Monitoring RBP and KIM-1 may help identify early tubular alterations and support clinical assessment, but further validation is needed.