Serum and Urinary Galectin-3 as a Non-Invasive Marker of Renal Fibrosis in Patients with Lupus Nephritis: A Cross-Sectional Controlled Study

Background Kidney fibrosis (KF) is a key determinant of adverse outcomes in lupus nephritis (LN). Although kidney biopsy remains the diagnostic gold standard, its invasiveness limits its routine use, necessitating the development of reliable non-invasive biomarkers. Galectin-3 (Gal-3), a β-galactoside-binding lectin involved in fibrogenesis, has been proposed as a candidate marker; however, its clinical value in LN remains uncertain. Objectives Our aim was to evaluate serum/urinary Gal-3 as non-invasive biomarkers of kidney fibrosis in LN and compare their diagnostic performance with non-nephritic systemic lupus erythematosus (SLE) and healthy controls. Methods This cross-sectional case-control study enrolled 150 participants (50 LN, 50 non-LN SLE, 50 controls). LN patients were stratified by interstitial fibrosis and tubular atrophy (IFTA) score. Subsequently, we measured serum/urinary Gal-3, renal function indices, C3, C4, anti-dsDNA, BMI, and urinary protein-to-creatinine ratio (UPCR). Disease activity was assessed using the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). Results Unlike the other groups, serum/urinary Gal-3 levels were significantly higher in the LN group (p < 0.001). Both correlated strongly with IFTA score (ρ = 0.76–0.81, p < 0.001) and moderately with SLEDAI. Urinary Gal-3 showed superior diagnostic accuracy for moderate–severe fibrosis (AUC = 0.87, 95% CI 0.77–0.98) than serum (AUC = 0.74). Both remained independent predictors of fibrosis severity after adjustment. Conclusions Serum/urinary Gal-3 are reliable, non-invasive biomarkers of kidney fibrosis in LN, with urinary Gal-3 demonstrating the highest diagnostic performance.