Optimal Proteinuria Target for Renoprotection in Patients with IgA Nephropathy

Background: Proteinuria is a target for renoprotection in kidney diseases. However, optimal level of proteinuria reduction in IgA nephropathy (IgAN) is unknown. Methods: We conducted a retrospective observational study in 500 patients with biopsy-proven IgAN. Time-averaged proteinuria (TA-P) was calculated as the mean of every 6 month period of measurements of spot urine protein-to-creatinine ratio. The study endpoints were a 50 % decline in estimated glomerular filtration rate (eGFR), onset of end-stage renal disease (ESRD), and slope of eGFR. Results: During a median follow-up duration of 65 (12–154) months, a 50 % decline in eGFR occurred in 1 (0.8%) patient with TA-P of,0.3 g/g compared to 6 (2.7%) patients with TA-P of 0.3–0.99 g/g (hazard ratio, 2.82; P = 0.35). Risk of reaching a 50 % decline in eGFR markedly increased in patients with TA-P of 1.0–2.99 g/g (P = 0.002) and those with TA-P$3.0 g/g (P, 0.001). ESRD did not occur in patients with TA-P,1.0 g/g compared to 26 (20.0%) and 8 (57.1%) patients with TA-P of 1.0– 2.99 and $3.0 g/g, respectively. Kidney function of these two groups deteriorated faster than those with TA-P,1.0 g/g (P, 0.001). However, patients with TA-P of 0.3–0.99 g/g had a greater decline of eGFR than patients with TA-P,0.3 g/g (2 0.4161.68 vs. 20.7362.82 ml/min/1.73 m2/year, P = 0.03). Conclusion: In this study, patients with TA-P,1.0 g/g show favorable outcomes. However, given the faster eGFR decline i