Repeat kidney biopsy in patients with ANCA-associated vasculitis and suspected kidney relapse

The role of repeat kidney biopsy in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) with suspected renal relapse remains uncertain. Clinical indicators such as hematuria, proteinuria and ANCA reappearance often guide therapy but may not reliably distinguish active vasculitis from chronic damage. Repeat biopsy may also provide prognostic information in patients with prolonged immunosuppressive exposure.

We retrospectively analyzed adults with biopsy-proven AAV who underwent a second kidney biopsy (KB2) for suspected renal relapses. Clinical, laboratory and histopathologic data from the first (KB1) and KB2 were reviewed. Dynamic variations in ANCA, hematuria and proteinuria between 6 months post-KB1 and -KB2 were assessed for their association with histologic activity.

Forty patients were included; 25 (62%) had histologically active vasculitis on KB2, whereas 15 (38%) showed inactive lesions. Active disease was associated with the presence (P = .001) and higher levels of hematuria [100 (92-100) vs 14 (4-46) cells/mm³, P < .0001] and proteinuria [1.55 (1.0-3.30) vs 0.89 (0.44-1.53) g/g, P = .046]. Longitudinally, ANCA and hematuria reappearance were associated with active vasculitis in 68% and 80% of cases, respectively, whereas proteinuria rise was not. Repeat biopsies showed a shift from proliferative to sclerotic lesions, with increased glomerulosclerosis and interstitial fibrosis; the degree of glomerulosclerosis inversely correlated with renal recovery at 6 months.

Clinical and laboratory findings alone often overestimate renal relapses. Dynamic changes in ANCA and hematuria improve prediction but remain insufficient to replace biopsy confirmation, which provides essential diagnostic and prognostic information in relapsing AAV.