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

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).

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.

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.

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.