#6260 PREDICTING KIDNEY FUNCTION AND END-STAGE KIDNEY DISEASE IN ANCA-ASSOCIATED VASCULITIS USING ANCA, C-REACTIVE PROTEIN AND C3
Authors: Domingues Patrícia , Inácio António Silva , Piedade Ana , Verde Ricardo , Duarte Jesuína , Santos Patricia Valério , Soto Karina , Cunha Liliana 
Published: June 2023

Abstract

Background and Aims
Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) are systemic autoimmune diseases that involve small- and medium-sized blood vessels. AAV compromises the overall survival of patients, and its kidney involvement can lead to end-stage kidney disease (ESKD). Our aim was to determine whether the serum C3, C-reactive protein (CRP) and ANCA levels could predict kidney survival.

Method
We retrospectively reviewed patients with AAV and kidney involvement (n = 62) from 2006 to 2022. Demographic, clinical and laboratory data were collected. Patients’ ANCA title were measured by ELISA, and Glomerular Filtration Rate (GFR) was estimate by CKD-EPI equation. ANCA, C3 and CRP were measure at diagnosis, remission, and last follow-up. ANCA was analyzed as continuous and categorical variable. We analyzed factors associated with dialysis dependency at diagnosis and evolution to ESKD. Multivariable adjusted Cox regression analysis was performed for assessing predictive variables associated with dialysis outcome.

Results
The cohort included 62 total patients, with median age of 69 (63-77) years old, 44% were female, 35.5% (n = 22) presented with alveolar haemorrhage, 82.3% (n = 51) were MPO-ANCA+ and 4 patients had concomitant anti-GBM+. At admission, the median ANCA title was 80.5 UI/mL (36.75- 112.25), C3 was 108.5 mg/dL (90-130.25) and CRP 7.5 mg/dL (2.14-14.34). The GFR was 11.17±11.16 at admission and 24% of patients required dialysis at admission (n = 15). At 3 months 30% (n = 19) required dialysis, 10% at 6 months (n = 6) and 5% at 1 year (n = 3). The median time until dialysis was 488.98 (0-5702) days. Twenty (32.3%) patients died during the study period. The title of ANCA at admission, as categorical variable, did not associate with requirement of kidney replacement therapy during follow-up (p = 0.870) nor as a continuous variable (p = 0.523). Considering C3 and CRP, only low C3 at last follow-up correlates with ESKD (p = 0.028). Median C3 at last follow-up was 91.5 mg/dl (79.5-107) in ESKD patients and 114.5 mg/dl (92-142.75) in patients that do not require dialysis. In the cox regression analysis of kidney survival, C3 levels at last follow-up were significantly associated with a shorter time until dialysis (p = 0.006). In a multivariate analysis, including age and gender, C3 levels at last follow-up lost significance to predict time until ESKD (p = 0.083, model p = 0.005). Initial GFR was not correlated with ANCA title at admission (r = 0.220, p = 0.205) nor as a categorical variable (p = 0.592). At remission, GFR was not correlated with ANCA title (r = 0.383, p = 0.349). Considering factors associated with the need for dialysis at admission, only CRP levels at admission were significantly higher (p = 0.035) in those who required dialysis. ANCA title and C3 at admission did not correlate with dialysis at admission (p = 0.875, p = 0.702). In multivariate analysis, including age and gender, CRP maintain its significancy (p = 0.036, model p = 0.044).

Conclusion
C3 and CRP levels have been studied as possible factors predicting kidney survival, however, results are not consistent. CRP is a marker of inflammation and C3 represents complement activity, these serologic markers could be important to identify patients at risk for ESKD. In our study CRP levels seems to be related to dialysis requirement at admission. These patients should be followed more closely and carefully to improve kidney survival.