Histopathologic and clinical predictors of kidney outcomes in ANCA-associated vasculitis

Background: A predictive histologic classification recently was proposed to determine the prognostic value of kidney biopsy in patients with antineutrophil cytoplasmic antibody-associated renal vasculitis (AAV).

Study design: A dual-purpose retrospective observational cohort study to assess the reproducibility of the new classification and clinical variables that predict outcomes.

Setting & participants: 169 consecutive patients with AAV were identified; 145 were included in the reproducibility study, and 120, in the outcomes study.

Predictor: Kidney biopsy specimens were classified according to the predominant glomerular lesion: focal, mixed, crescentic, and sclerotic. An assessment of tubular atrophy also was performed.

Outcomes: The primary outcome was time to end-stage kidney disease or all-cause mortality, modeled using Cox regression analysis.

Measurements: Estimated glomerular filtration rate, requirement for renal replacement therapy.

Results: For the reproducibility study, the overall inter-rater reliability of the classification demonstrated variability among 3 histopathologists (intraclass correlation coefficient, 0.48; 95% CI, 0.38-0.57; κ statistic=0.46). Although agreement was high in the sclerotic group (κ=0.70), it was less consistent in other groups (κ=0.51, κ=0.47, and κ=0.23 for crescentic, focal, and mixed, respectively). For the clinical outcomes study, patients with sclerotic patterns of glomerular injury displayed the worst outcomes. Patients with focal (HR, 0.26; 95% CI, 0.12-0.58; P=0.001), crescentic (HR, 0.33; 95% CI, 0.16-0.69; P=0.003), and mixed (HR, 0.39; 95% CI, 0.18-0.81; P=0.01) patterns of injury had lower risk of the primary outcome. Tubular atrophy correlated with outcome, and advanced injury was associated with worse outcomes (HR, 5.9; 95% CI, 2.25-15.47; P<0.001). Level of kidney function at presentation strongly predicted outcome (HR per 10-mL/min/1.73m(2) increase in estimated glomerular filtration rate, 0.63; 95% CI, 0.46-0.81; P<0.001).

Limitations: Data availability, given the retrospective nature of the study.

Conclusions: Reproducibility of the classification was seen only in patients with sclerotic patterns of glomerular injury. Sclerotic pattern of glomerular injury, advanced chronic interstitial injury, and decreased kidney function all predicted poor outcomes.