Proteinuria Reduction and Kidney Survival in Focal Segmental Glomerulosclerosis

Rationale & Objective: Remission of proteinuria has been shown to be associated with lower rates of kidney disease progression among people with focal segmental glomerulosclerosis (FSGS). The goal of this study was to evaluate whether reductions in proteinuria after treatment are associated with greater kidney survival. Study Design: Cohort analysis of clinical trial participants. Setting & Participants: Patients with steroid-resistant FSGS enrolled in a randomized treatment trial that compared cyclosporine with mycophenolate mofetil plus dexamethasone. Predictors: Reduction in proteinuria measured during 26 weeks after initiating treatment. Outcomes: Repeated assessments of estimated glomerular filtration rate (eGFR) and time to a composite outcome of kidney failure or death assessed between 26 weeks and 54 months after randomization. Analytical Approach: Multivariable linear mixed-effects models with participant-specific slope and intercept to estimate the association of change in proteinuria over 26 weeks while receiving treatment with the subsequent slope of change in eGFR. Multivariable time-varying Cox proportional hazards models were used to estimate the association of changes in proteinuria with time to the composite outcome. Results: 138 of 192 trial participants were included. Changes in proteinuria over 26 weeks were significantly related to eGFR slope. A 1-unit reduction in log-transformed urinary protein-creatinine ratio was associated with a 3.90 mL/min/1.73 m² per year increase in eGFR (95% CI, 2.01-5.79). This difference remained significant after adjusting for complete remission. There was an analogous relationship between time-varying proteinuria and time to the composite outcome: the HR per 1-unit reduction in log-transformed urinary protein-creatinine ratio was 0.23 (95% CI, 0.12-0.44). Limitations: Limited to individuals with steroid-resistant FSGS followed up for a maximum of 5 years. Conclusions: These findings provide evidence for the benefit of urinary protein reduction in FSGS. Reductions in proteinuria warrant further evaluation as a potential surrogate for preservation of kidney function that may inform the design of future clinical trials.