Impact of baseline proteinuria level on long-term outcomes in lupus nephritis

Objectives Proteinuria is a marker of lupus nephritis (LN) activity and damage. We aimed to explore the impact of baseline proteinuria level on long-term outcomes. Methods We included 249 patients diagnosed with their first biopsy-proven LN. We divided patients based on baseline proteinuria into low-level (≤1 g/day, group 1; 62 patients), moderate-level (>1 and <3 g/day, group 2; 90 patients), and high-level proteinuria (≥3 g/day, group 3; 97 patients). Outcomes included complete proteinuria recovery (CPR) at 1 year, an adverse composite outcome (ESKD, a sustained ≥40% decline in eGFR, or death), and LN flares. Cox proportional hazard models were used to examine the association between baseline characteristics and long-term outcomes. Results At baseline, the median [IQR] age was 33.2 [26.4, 42.4] years; median proteinuria level was 2.2 [1.0, 3.8] g/day. 177 (71%) patients had proliferative lesions on biopsy; 59.7% in group 1, 78.9% in group 2, and 71.4% in group 3. The rate of achievement of CPR at 1 year was highest for group 1 and lowest for group 3. For long-term outcomes (median follow-up 8.4 years), the frequency of the adverse composite outcome was 27.4%, 26.7%, and 48.5% in groups 1, 2, and 3, respectively; p= 0.003. The corresponding frequency of flares was 27.4%, 38.2%, and 61.9%, respectively; p< 0.001. In the multivariable model for factors associated with long-term outcomes, there was no significant difference between groups 1 and 2; group 3 was associated with the worst prognosis. Conclusions Low-level proteinuria is commonly associated with proliferative LN and adverse long-term outcomes.