Background and objectivesThe histopathologic classification for ANCA-associated GN distinguishes four classes on the basis of patterns of injury. In the original validation study, these classes were ordered by severity of kidney function loss as follows: focal, crescentic, mixed, and sclerotic. Subsequent validation studies disagreed on outcomes in the crescentic and mixed classes. This study, driven by the original investigators, provides several analyses in order to determine the current position of the histopathologic classification of ANCA-associated GN.Design, setting, participants, & measurementsA validation study was performed with newly collected data from 145 patients from ten centers worldwide, including an analysis of interobserver agreement on the histopathologic evaluation of the kidney biopsies. This study also included a meta-analysis on previous validation studies and a validation of the recently proposed ANCA kidney risk score.ResultsThe validation study showed that kidney failure at 10-year follow-up was significantly different between the histopathologic classes (P<0.001). Kidney failure at 10-year follow-up was 14% in the crescentic class versus 20% in the mixed class (P=0.98). In the meta-analysis, no significant difference in kidney failure was also observed when crescentic class was compared with mixed class (relative risk, 1.15; 95% confidence interval, 0.94 to 1.41). When we applied the ANCA kidney risk score to our cohort, kidney survival at 3 years was 100%, 96%, and 77% in the low-, medium-, and high-risk groups, respectively (P<0.001). These survival percentages are higher compared with the percentages in the original study.ConclusionsThe crescentic and mixed classes seem to have a similar prognosis, also after adjusting for differences in patient populations, treatment, and interobserver agreement. However, at this stage, we are not inclined to merge the crescentic and mixed classes because the reported confidence intervals do not exclude important differences in prognosis and because an important histopathologic distinction would be lost.

Background Renal fibrosis is the hallmark of chronic kidney disease (CKD) and characterized by an imbalanced extracellular matrix remodeling. Endotrophin (ETP) is a signaling molecule released from collagen type VI (COL VI). ETP can be measured by the PRO-C6 assay, which quantifies the levels of COL VI formation. ETP levels were previously associated with mortality and disease progression in patients with CKD. We hypothesized that serum and urinary ETP levels correlate with the degree of interstitial fibrosis in kidney biopsies from patients with IgA nephropathy (IgAN) and patients with ANCA-associated vasculitis (AAV). Methods We examined a cohort of 49 IgAN and 47 AAV patients. A validation cohort of 85 IgAN patients was included. ETP was measured in serum (S-ETP) and urine (U-ETP/Cr) samples, taken on the same day before renal biopsy was performed, using the ELISA PRO-C6. The biopsies were evaluated for interstitial fibrosis and tubular atrophy according to the Banff and MEST-C scores. Results S-ETP and U-ETP/Cr levels correlated with kidney function, increased with CKD severity, correlated with the extent of interstitial fibrosis and gradually increased with increasing degree of interstitial fibrosis and tubular atrophy. ETP outperformed the known fibrosis biomarker Dickkopf-3 for discrimination of patients with high fibrotic burden. The association of S-ETP and U-ETP/Cr with the level of kidney fibrosis was confirmed in the validation cohort. Conclusions We demonstrated that high levels of circulating and excreted ETP are not only indicative of lower kidney function, but also reflect the burden of fibrosis in the kidneys.

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Anti-glomerular basement membrane (GBM) disease is a rare, aggressive vasculitis with no validated prediction tools to assist its management. We investigated a retrospective multicenter international cohort with the aim to transfer the Renal Risk Score (RRS) and to identify patients that benefit from rescue immunosuppressive therapy.Of a total 191 patients, 174 patients were included in the final analysis (57% female, median age 59 years). Using Cox and Kaplan-Meier methods, the RRS was found to be a strong and effective predictor for end stage kidney disease (ESKD) with a model concordance of C=0.760. The 36-month renal survival was 100%, 62.4%, and 20.7% in the low-, moderate-, and high-risk groups, respectively (P<0.001). The need for renal replacement therapy (RRT) at diagnosis and the percentage of normal glomeruli in the biopsy were independent predictors of ESKD (P<0.001, P<0.001).Considering the 129 patients initially requiring RRT, the best predictor for renal recovery was the percentage of normal glomeruli (C=0.622; P<0.001), a split either side of 10% providing good stratification. A model with the predictors RRT and normal glomeruli (N) achieved superior discrimination (C=0.840, P<0.001). Dividing patients into four risk groups led to a 36-month renal survival of 96.4% (no RRT, N≥10%), 74.0% (no RRT, N<10%), 42.3% (RRT, N≥10%) and 14.1% (RRT, N<10%), respectively.In summary, we demonstrate that the RRS concept is transferrable to anti-GBM disease. Stratifying patients according to the need for RRT at diagnosis and renal histology improves prediction, highlighting the importance of normal glomeruli. Here, we propose a stratification to assist in the management of anti-GBM disease.

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