Clinical and histological findings at second but not at first kidney biopsy predict end-stage kidney disease in a large multicentric cohort of patients with active lupus nephritis.

Objective: To investigate second kidney biopsy as predictor of end-stage kidney disease (ESKD) in active lupus nephritis (LN).

Methods: Patients with biopsy-proven LN (International Society of Nephrology/Renal Pathology Society 2003) who had undergone a second kidney biopsy between January 1990 and December 2018 were included. Clinical and histological findings at first and at second biopsy were analysed with Cox proportional hazard models to predict ESKD, defined as start of kidney replacement therapy. Survival curves were calculated with Kaplan-Meier method.

Results: Ninety-two patients with LN were included, 87% females, mean follow-up 17.9±10.1 years. Reasons for second kidney biopsy encompassed nephritic flares (n=28, 30.4%), proteinuric flares (n=46, 50%) or lack of renal response (n=18, 19.5%). Class switch from first biopsy occurred in 50.5% of cases, mainly from non-proliferative towards proliferative classes. Class IV remained stable in over 50% of cases. Twenty-five patients (27.2%) developed ESKD, mostly belonging to the nephritic flare group (17/28, 60.7%). Independent predictors of ESKD at second biopsy were activity index (AI; (HR 95% CI) 1.20 (1.03 to 1.41), p=0.022), chronicity index (CI; 1.41 (1.09 to 1.82), p=0.008) and 24h-proteinuria (1.22 (1.04 to 1.42), p=0.013). AI≥2 (log-rank p=0.031), CI >4 (log-rank p=0.001) or proteinuria ≥3.5 g/day (log-rank=0.009) identified thresholds for higher ESKD risk. In a subgroup analysis, glomerular activity and tubular chronicity mostly accounted for AI and CI association with ESKD. No histological or laboratory predictors emerged at first biopsy (95% CI): AI: 0.88 to 1.19; CI: 0.66 to 1.20; proteinuria 0.85 to 1.08.

Conclusions: Findings at second but not at first kidney biopsy in patients with persistently active or relapsing LN inform about ESKD development in a long-term follow-up.