Utility of Non-albumin Proteinuria for the Assessment of the Severity of Tubulointerstitial Inflammation in Lupus Nephritis Patients.

Background Lupus nephritis (LN) is the most common severe manifestation of systemic lupus erythematosus (SLE) that can involve all kidney components. The International Society of Nephrology/Renal Pathology Society (ISN/RPS) 2003 lupus nephritis classification only focuses on glomerular involvement, although tubulointerstitial inflammation (TI) is a better predictor of renal failure.  Objective To determine the association of non-albumin proteinuria (NAP) and severity of tubulointerstitial inflammation in lupus nephritis patients.  Methods This cross-sectional study was carried out in the Department of Nephrology of Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh. A total of eighty (80) LN patients were enrolled in this study. Their urinary protein-to-creatinine ratio (uPCR), urinary albumin-to-creatinine ratio (uACR), renal biopsy, and relevant routine investigations were done accordingly. Urinary non-albumin proteinuria (uNAP) was measured by subtracting uACR from uPCR. Data were analyzed and compared by statistical tests.  Results Among 80 lupus nephritis patients, 39 (48.8%) had no-to-mild tubulointerstitial inflammation (TI), whereas 41 (51.2%) had moderate-to-severe tubulointerstitial inflammation. Proliferative glomerulonephritis (GN) (class III/class IV) was observed in 48 patients (60%), while non-proliferative GN (class II/V) was present in 32 patients (40%). In the logistic regression analysis, non-albumin proteinuria (uNAP) was found to be associated with moderate-to-severe tubulointerstitial inflammation (OR: 3.166, 95% CI: 1.145-8.757, p=0.026). The calculated cutoff value for uNAP was 887, which corresponds to a sensitivity of 96.7% and specificity of 76.0% (p<0.001).  Conclusion Non-albumin proteinuria is associated with the severity of tubulointerstitial inflammation in lupus nephritis. Therefore, assessing non-albumin proteinuria can offer clinically valuable insights into the management of lupus nephritis.