Urinary podocin; is it a valuable disease activity biomarker in patients with lupus nephritis?

Introduction: Podocyturia can be considered as a noninvasive marker for evaluation and follow up of glomerular disease progression. Objectives: In this study, we aimed to assess the clinical utility of urinary podocin as an index of lupus nephritis activity. Patients and Methods: This cross-sectional study included 45 patients with systemic lupus erythematosus (SLE). Patients were subdivided into three groups: group (I) 10 SLE, patients without clinical or laboratory evidence of lupus nephritis (LN), which were assessed by Systemic Lupus Activity Measure (SLAM) score of the disease activity. Group (II), which included 15 patients with evident active LN before starting the immunosuppressive induction treatment and group (III) which is consisted of 20 patients with LN in partial or complete remission. Urinary podocin assay was conducted by enzyme-linked immunosorbent assay enzyme-linked immunosorbent assay (ELISA) technique. Results: There was a statistically significant difference between the studied groups regarding urinary podocin levels. The mean of urinary podocin (ng/mL) was (2.29 ± 0.71, 37.20 ± 14.38, 10.5 ±2.30; P≤0.001) in the three groups consecutively, with significant decrease of urinary podocin in LN patients after remission versus high level in patients with active LN. Highly significant positive correlations were found between urinary podocin and global SLAM activity (r = 0.852; P≤ 0.001), SLAM-Renal score (r= 0.854; P≤0.001), urine albumin to creatinine ratio, (mg/g) (r=0.895; P≤0.001). Highly significant negative correlations of urinary podocin and C3 (r=0.803; P≤ 0.001), C4 (r= -0.760; P≤0.001) and eGFR (r = -0.759; P≤0.001) were detected. Conclusion: Urinary podocin as non-invasive biomarker is significantly correlated to SLE disease activity and LN activity measured by global SLAM clinical score with both high sensitivity and specificity. Urinary podocin can be also considered as a prognostic marker in the management of LN patients.