#933 Serum and kidney complement and severity of ANCA associated vasculitis in the kidney

Abstract Background and Aims Kidney involvement in ANCA associated vasculitis (AAV) is commonly described as pauci-immune based on histological characteristics. However, we now know that the complement system is activated and contributes to the pathogenesis of AAV – with Avacopan (C5a inhibitor) demonstrating superior efficacy in maintenance of remission over Prednisolone in the ADVOCATE trial. Our aim was to evaluate if there is an association between kidney disease severity and the presence of serum and histological complement activation markers. Method Retrospective cohort study of 59 patients with AAV diagnosed between November 2015 and May 2019. Complement activation markers were serum complements (C3 and C4) levels and presence of complement (C3, C1q and C4) in glomerular capillary walls in immunofluorescence with intensity of 2+ and 3+. Kidney disease severity markers were peak serum creatinine value at presentation, anti-MPO or anti-PR3 levels, and number and proportion of glomeruli with crescents on kidney biopsy. Associations were evaluated using Spearman correlation or Mann Whitney U test as appropriate Results Among 59 patients with biopsy-proven AAV in the kidney, the median (25th percentile, 75th percentile) age was 68.8 (60.7, 73.4) years, serum creatinine was 263 (156, 560) µmol/L, and anti-MPO and anti-PR3 levels were 100.0 (81.5, 199.2) and 128.8 (22.9, 200) in 41 and 7 patients, respectively. respectively. The number and proportion of glomeruli with crescents were 6 (3, 12) and 33.3% (12.0%, 42.6%), respectively. Serum C3 and C4 were performed in 41 patients and the median levels were 1.00 (0.83, 1.14) and 0.24 (0.18, 0.31), respectively. Serum C3 level did not correlate with serum creatinine, anti-MPO or anti-PR3 titers, and number and proportion of glomeruli with crescents. Serum C4 level was negatively correlated with anti-MPO titer (34 patients; r = −0.393, p = 0.02) but did not correlate with serum creatinine or number or proportion of crescents. Complement in the glomerular capillary wall was present in 8 patients (13.6%): C3, C1q and C4 were present in 8, 3 and 1 patients, respectively. Serum creatinine median 299 (IQR 133, 998) µmol/L versus 261 (156, 359) µmol/L, p = 0.39, anti-MPO titer 100 (88.3, 200) IU/ml versus 100 (79.4, 198) IU/ml, p = 0.74, number of crescents 14 (4, 21) versus 5 (3, 12), p = 0.90 and proportion of crescents 38.9% (12.5%, 42.3%) versus 31.3% (11.1%, 44.3%), p = 0.59 were not different in those with and without complement in the kidney biopsy. Conclusion The presence of complement activation markers was not associated with kidney disease severity in AAV. However, the detection of clinically significant associations may have been limited by our cohort size.