Urinary Liver‐Type Fatty Acid‐Binding Protein, Albuminuria, and eGFR Trajectories in Type 2 Diabetes

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Abstract
Background: Urinary liver‐type fatty acid‐binding protein (L‐FABP) reflects proximal tubular stress and has been proposed as a biomarker of diabetic kidney disease. We examined whether urinary L‐FABP provides information on longitudinal kidney function beyond urinary albumin‐to‐creatinine ratio (UACR). Methods: This retrospective cohort study included patients with type 2 diabetes who had UACR and urinary L‐FABP measured simultaneously at the initial visit and underwent outpatient follow‐up. The analysis included patients with at least three eGFR measurements over at least 2 years. eGFR trajectories were evaluated using linear mixed‐effects models with random intercepts and slopes. UACR and L‐FABP were analyzed as log(1 + x )‐transformed continuous variables. Results: The analysis included 1,031 patients (age 58.1 years; 65.1% men), with a median follow‐up of 4.76 years and a median of 10 eGFR measurements. Urinary L‐FABP correlated with UACR (Spearman ρ = 0.526; p < 0.001). Both biomarkers were independently associated with lower baseline eGFR. In a model without UACR, higher L‐FABP was associated with faster eGFR decline (−0.98 mL/min/1.73 m²/year per unit increase in log[1 + L‐FABP]; p < 0.001). After adjustment for continuous UACR, the association was attenuated and no longer significant (−0.19; 95% CI, −0.49 to 0.11; p = 0.221), whereas UACR remained independently associated with eGFR decline. Results were unchanged after further adjustment for baseline eGFR and lipid parameters. Conclusions: Urinary L‐FABP was associated with baseline kidney impairment but did not independently predict eGFR trajectory after continuous UACR was taken into account. Urinary L‐FABP reflects kidney injury severity, although its incremental prognostic value beyond quantitatively assessed albuminuria was limited in this cohort.

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