Albuminuria after induction treatment and kidney prognosis in ANCA-associated glomerulonephritis

Introduction It remains unclear whether persisting proteinuria in ANCA-associated glomerulonephritis (AAGN) reflects damage from the initial injury or ongoing inflammation. Methods A retrospective, single-centre study of biopsy-proven AAGN was performed. The study defined the 'albuminuria' group as urine albumin-to-creatinine ratio (ACR) >300 mg/g and the 'no albuminuria' group as ACR <= 300 mg/g at 6 months. We sought the clinical and histopathological characteristics of both the initial and subsequent biopsies and long-term kidney outcomes stratified by albuminuria levels. Results Two hundred and eighteen patients were included. Within the first 6 months, 28 (13%) died or progressed to end-stage kidney disease (ESKD). Among the remaining 190 patients, 37% had an ACR >300 mg/g at 6 months. The albuminuria group more frequently presented with a Berden mixed or crescentic class and had higher glomerular activity on the initial biopsy. They were more often male (OR 2.75; 95% CI 1.15-6.54), younger age (OR 0.96; 95% CI 0.93-0.99), and had fewer normal glomeruli in the biopsy (OR 0.96; 95% CI 0.93-0.99) compared with the group without albuminuria. Over the initial 5-year period, the recovery in eGFR was lower in the albuminuria group (adjusted mean difference in Delta eGFR -12.5 mL/min per 1.73 m(2); 95% CI -15.8 to -9.1). In multivariable analysis, ACR >300 mg/g was associated with a higher risk of ESKD, even after adjusting for Berden classification and eGFR at diagnosis (hazard ratio 6.53; 95% CI 1.49-28.50). Conclusions In a well-defined cohort of AAGN, one-third of the patients, primarily younger males with a lower percentage of normal glomeruli, had persisting albuminuria after induction treatment which was associated with worse kidney outcomes independent of Berden class and eGFR at diagnosis.