Non-albumin proteinuria as a parameter of tubulointerstitial inflammation in lupus nephritis

Tubulointerstitial inflammation (TI) has prognostic significance in the renal outcomes of lupus nephritis. Here, we aimed to determine whether non-albumin proteinuria is associated with TI severity and with the renal response in lupus nephritis. We included patients with biopsy-confirmed lupus nephritis at a tertiary medical center in Korea from January 2011 to April 2017. Patients in whom the urine protein/creatinine ratio (uPCR) and the urine albumin/creatinine ratio (uACR) were measured simultaneously were included. Laboratory data and renal pathology were reviewed. Non-albumin proteinuria was calculated by subtracting uACR from uPCR. The renal response was assessed by the amount of proteinuria present at 6 months after treatment with immunosuppressants. Logistic regression analyses were performed to identify factors associated with TI severity and renal response. Out of 45 patients, 36 (80%) had no-to-mild TI, whereas 9 (20%) had moderate-to-severe TI. Proliferative (class III ± V/IV ± V) and nonproliferative (class II/V) glomerulonephritis (GN) were present in 38 (84.4%) and 7 (15.6%) patients, respectively. In the logistic regression analyses, non-albumin proteinuria (uPCR - uACR) was associated with moderate-to-severe TI (odds ratio [OR] 3.166, 95% confidence interval [95% CI] 1.145-8.757, p = 0.026) and was inversely associated with complete renal response (adjusted OR 0.180, 95% CI 0.045-0.718, p = 0.015). In lupus nephritis, non-albumin proteinuria was associated with TI severity and with poor renal response after immunosuppressive treatment. Thus, the determination of non-albumin proteinuria can provide clinically valuable information on lupus nephritis.