P0276SERUM C3 LEVELS AND THE PROGNOSIS OF ANCA-ASSOCIATED VASCULITIS: A SINGLE-CENTER RETROSPECTIVE STUDY
Authors: Carta Annalisa , Russo Elisa , Cipriani Leda , Picciotto Daniela , Saio Michela , Costigliolo Francesca , Verzola Daniela , Garibotto Giacomo , Sanna Alberto , Esposito Pasquale , Paoletti Ernesto , Viazzi Francesca 
Published: June 2020

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Background and Aims
Despite improved survival, patients affected by ANCA-associated vasculitis (AAV) presenting with rapidly progressive glomerulonephritis (RPGN) still remain at a higher risk of death relative to the general population. Recent findings suggest a role for the activation of the complement alternative pathway in the pathogenesis of the disease. We aimed to retrospectively evaluate the presentation and outcome of a cohort of patients with AAV and RPGN according to ANCA specificity, investigating the role of complement pathways.

Method
We retrospectively examined 1,547 biopsies performed between 1996 and 2019 in our center, which included 124 patients presenting with paucimmune RPGN. Patients without ANCA serology and/or with missing data (n=44), ANCA negative RPGN (n=15) and anti-GBM disease (n=2) were excluded from our analysis. Seventy-eight patients with AAV and RPGN (63 biopsy proven) were analysed and compared according to ANCA serotype (n=30 MPO, n=21 PR3). Furthermore, data were analysed on the basis of median levels of serum C3 (1.05 g/l).
Statistical analysis Data are mean ± SD or median and interquartile range for variables not normally distributed. Groups were compared using ANOVA after logarithmic transformation of skewed variables. Primary endpoint was renal survival defined as need for renal replacement therapy (NRRT); secondary outcome was patient survival. Cumulative and renal survivals were calculated using Kaplan-Meier method and differences between groups were analysed with the log-rank test. Multivariate Cox proportional hazard analysis for time to NRRT was performed to determine the significance of different risk factors in renal outcome. A p value of &lt; 0.05 was considered statistically significant.

Results
Patients had a mean age of 64± yrs and eGFR ±15 ml/min at diagnosis. Patients with MPO-AAV were older (69±11 vs. 61±14 yrs, p=0.02) and showed lower levels of C3 (1.0±0.22 vs 1.25±0.2 g/l, p=0.009) as compared to PR3 patients. Moreover, those presenting with C3 levels lower than median value had more advanced renal damage at diagnosis (eGFR 7± ml/min vs 15.5± ml/min, p= 0.04). Serum C3, but not C4 levels, significantly correlated with eGFR, proteinuria and serum uric acid at diagnosis. Twenty-seven (39.7%) reached ESRD requiring RRT. The 1-, 5- and 10- yrs patients renal survivals were 81%, 62.9 % and 52.4%. Renal outcome was neither influenced by ANCA serotype nor gender but patients with C3 levels below median value exhibited a worse renal prognosis (Log rank p=0.02) and a 5 times higher risk of NRRT (HR 5.1, 95% CI 1.4-18.7, p=0.01) independently by potential confounding factors.

Conclusion
Referral to the nephrologist was late, at an advanced stage of disease, indicating the need to improve the awareness of AAV and RPGN in order to favour early treatment. In this cohort, low C3 indicated a more severe renal damage and predicted poorer renal outcome thus suggesting a role of complement activation in the pathogenesis and progression of these nephritides.