Verification of the Utility of Urinary L-FABP as a Predictor of Impaired Renal Function Based on Its Relationship with Changes in Renal Function

Background: In patients with diabetes or hypertension, if appropriate intervention is not initiated early in the course of kidney disease, not only does the risk of progressing to end-stage renal failure increase, but mortality associated with vascular complications also rises as the disease progresses; therefore, there is an urgent need to develop urinary biomarkers that enable early diagnosis and prediction of disease progression. Methods: This two-year prospective observational study involved 185 outpatients. Patients were classified into two groups based on their baseline urinary L-FABP levels relative to the reference value of 8.4 μg/g·Cr at the start of the study. The rate of eGFR decline during the observation period was evaluated. Results: The results showed an interaction (synergistic effect) between urinary L-FABP and time in patients with diabetes or hypertension who had an eGFR of at least 60 mL/min/1.732 m2/kg/1.732 m2. Patients with high urinary L-FABP levels (>8.4 μg/g·Cr) exhibited a notably faster eGFR decline compared with those with low levels (≤8.4 μg/g·Cr). This finding suggests the potential of urinary L-FABP as a predictor of renal function decline; we evaluated this utility using the area under the ROC curve (AUC) and logistic regression analysis. The results indicate that urinary L-FABP holds potential as a predictor of renal function decline in diabetic or hypertensive patients with preserved eGFR. Conclusions: Among the analysis groups in which the validation was conducted, it was demonstrated that urinary L-FABP holds potential as a predictor of renal function decline in patients with diabetes or hypertension who have a maintained eGFR. Given that urinary L-FABP is thought to reflect tubulointerstitial damage associated with renal microcirculatory impairment, its future utility as a urinary biomarker for the early diagnosis and prognosis of chronic kidney disease (CKD) is anticipated.