Urinary biomarkers in the early diagnosis of diabetic kidney disease and diabetic retinopathy: A pilot study.

BACKGROUND: Diabetic kidney disease (DKD) and diabetic retinopathy (DR) are the most frequent microvascular complications of diabetes mellitus. Although microalbuminuria is a conventional early marker of DKD, its limited sensitivity and the growing recognition of nonalbuminuric DKD highlight the need for more sensitive early detection tools. Urinary biomarkers such as type IV collagen, transferrin, and liver-type fatty acid-binding protein (L-FABP) may capture early glomerular or tubular injury before the onset of overt albuminuria. This pilot study evaluated the diagnostic performance of these biomarkers in adults with type 2 diabetes mellitus (T2DM) and explored their associations with DR. METHODS: A cross-sectional per-protocol study included 80 T2DM patients and 10 healthy controls. Diabetic participants were categorised as normoalbuminuric (<30 mg/day) or microalbuminuric (30-300 mg/day). First-morning urine samples were used for final analyses. Urinary type IV collagen, transferrin, and L-FABP were quantified using ELISA and expressed in ng/mL. Group comparisons used t-tests or ANOVA for normally distributed variables, and Mann-Whitney U or Kruskal-Wallis tests for non-normally distributed data. Correlations were assessed using Pearson or Spearman coefficients. Diagnostic performance was analyzed using ROC curves. RESULTS: The cohort (55% male; mean age 59.85± 8.87 years) had similar BMI, smoking status, and eGFR across groups. Biomarker levels differed significantly among microalbuminuric, normoalbuminuric, and control groups (p<0.001): type IV collagen (0.97 vs. 0.55 vs. 0.48), transferrin (45.51 vs. 14.83 vs. 6.57), and L-FABP (480.15 vs. 228.08 vs. 89.91). Type IV collagen demonstrated the best diagnostic ability for early DKD (AUC 90.4%). DR was present in 24 patients (30%), and transferrin levels were significantly higher in those with DR (81.38 vs. 38.12 ng/mL; p=0.03). CONCLUSIONS: Urinary type IV collagen, transferrin, and L-FABP show promise for early DKD detection, while transferrin additionally correlates with DR. Larger studies are needed to confirm these findings.