The Role of Kidney Biopsy as a Tool for Personalized Treatment Decision-Making in Patients with Anti-Neutrophil Cytoplasmic Antibody (ANCA)-Associated Nephritis

<b>Background/Objectives</b>: Personalized treatment approaches are increasingly recognized as essential in the management of anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV), given the substantial heterogeneity in disease severity and patient characteristics. Kidney biopsy has the potential to serve as an effective tool for personalized treatment decision-making in patients with AAV. This study aimed to investigate the association of kidney biopsy with intensive immunosuppressive therapy and clinical outcomes in patients with AAV and kidney impairment. <b>Methods</b>: In this retrospective study, propensity score overlap weighting was applied to compare intensive immunosuppressive therapy and clinical outcomes (ESKD, death, combined ESKD and death, and infectious complications) between patients with AAV who underwent kidney biopsy and those who did not. <b>Results</b>: Out of 74 patients with AAV, 38 underwent kidney biopsy. Overlap weight analysis revealed that kidney biopsy was significantly associated with intensive immunosuppressive therapy (risk difference [RD], 28.9%; 95% confidence interval [CI], 0.017 to 0.562). Kidney biopsy was not associated with combined ESKD and death (RD, -0.2%; 95% CI, -0.302 to 0.298), death (RD, -3.8%; 95% CI, -0.264 to 0.189), ESKD (RD, -7.3%; 95% CI, -0.353 to 0.207), and infectious complications (RD, -25.9%; 95% CI, -0.537 to 0.020). <b>Conclusions</b>: In this observational cohort, kidney biopsy was associated with intensification of immunosuppressive therapy. However, after adjustment using overlap weighting, no statistically significant difference in clinical outcomes was detected, and the reduced effective sample size limited statistical power. These findings should be interpreted cautiously, as causal inference regarding the prognostic impact of kidney biopsy remains limited.