Urinary liver‐type fatty acid‐binding protein in clinically healthy elderly cats: Evaluation of its potential to detect IRIS stage 1 chronic kidney disease and borderline proteinuria

BACKGROUND: Urinary liver‐type fatty acid‐binding protein (uL‐FABP) is a promising biomarker to detect early chronic kidney disease (CKD) in cats. Few healthy cats show increased uL‐FABP for unknown reasons. OBJECTIVES: The objective of this study was to evaluate uL‐FABP in a large healthy elderly cat population comparing cats with and without International Renal Interest Society (IRIS) stage 1 CKD and with and without borderline proteinuria. METHODS: This was a cross‐sectional study. One hundred ninety‐six clinically healthy client‐owned cats of ≥7 years old were subdivided based on two criteria: (1) having either IRIS stage 1 CKD or no evidence of CKD and (2) having borderline proteinuria or no proteinuria. Urinary L‐FABP was measured using a validated commercially available feline L‐FABP ELISA. RESULTS: Overall, uL‐FABP was detectable in 6/196 (3%) healthy elderly cats. For the first subdivision, nine (5%) cats had IRIS stage 1 CKD, 184 cats had no evidence CKD and three cats were excluded. All cats with IRIS stage 1 CKD had uL‐FABP concentrations below the detection limit, whereas 6/184 (3%) cats without IRIS stage 1 CKD had detectable uL‐FABP concentrations (median 1.79 ng/ml, range 0.79–3.66 ng/ml). For the second subdivision, 47 (24%) cats had borderline proteinuria, 147 cats had no proteinuria and two cats were excluded. One of the borderline proteinuric cats had a detectable uL‐FABP concentration, whereas the other five cats with detectable uL‐FABP concentrations were non‐proteinuric. CONCLUSION: With the current assay, the screening potential of uL‐FABP as an early biomarker for feline CKD is limited as uL‐FABP was rarely detected in clinically healthy elderly cats independently of the presence of either IRIS stage 1 CKD or borderline proteinuria.