ARE PR3 ANTIBODY TITERS REALLY IMPORTANT FOR ROUTINE CLINICAL PRACTICE?. STUDY FROM A SINGLE UNIVERSITY HOSPITAL

V. Calvo-Río, S. Al Fazazi, M. Renuncio-García, M. Rodriguez Vidriales, C. Escagedo Cagigas, J. Irure-Ventura, L. Martín-Penagos, A. Herrero-Morant, M. Lopez-Hoyos, R. BlancoMarqués de Valdecilla University Hospital, Rheumatology, Santander, Spain Hospital Puerta Del Mar, Rheumatology, Cádiz, Spain Marqués de Valdecilla University Hospital, Immunology, Santander, Spain Marqués de Valdecilla University Hospital, Nephrology, Santander, Spain  Background Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA). Anti-proteinase 3 are one of the main ANCA subtypes. There are contradictory studies on the relation between ANCA levels and the severity of the disease and its prognosis [1]. Objectives In patients with positive anti-PR3 antibodies from a university hospital we assess: a) associated diseases, b) specificity in diagnosing AAV and, c) determine if there is a cut-off point that allows to correlate the levels of anti-PR3 antibodies with the severity and prognosis of AAV. Methods Observational study of patients with positive anti-PR3 from a University Hospital, from 2003 to 2022. ANCA was determined by chemiluminescence. The specificity of anti-PR3 for AAV diagnosis, predictive value of severity and prognosis were determined with Receiver Operating Characteristic (ROC) curves. At diagnosis, AAV with renal disease (hematuria and/or proteinuria) and lung involvement (hemoptysis, asthma and/or respiratory failure) were considered severe. During follow-up, the prognosis was considered worse if the patient needed dialysis, a transplant, or died. Results We study 54 patients with positive PR3. Most of them (81.5%) had an underlying AAV being the most frequent GPA (61.1%). The non vasculitic disease more frequent was Ulcerative colitis (11.1%). Table 1 summarizes the prevalence of these antibodies in different diseases. The frequencies are equivalent to those previously described and it is noteworthy the presence of anti-PR3 in drug-induced vasculitis, mainly by cocaine. Anti-PR3 antibodies for a diagnosis of vasculitis (n=44), an area under the curve (AUC) was calculated (AUC=0.7318), and a cut-off point of 20.5 IU/ml was determined (Figure 1). Significant differences in anti-PR3 levels were observed between those patients with renal or pulmonary dysfunction (n=30) and those without them (n=24) (p=0.0048), and a cut-off threshold of 41.5 IU/ml was established. Finally, after examining the illness’s prognosis an AUC= 0.5643 was obtained, being no significant differences between those patients who had a worse disease progression (n=14) and those who did not (n=40) (p=0.4847). Conclusion The presence of anti-PR3 is mainly associated with AAV, although in up to a fifth of cases it can be associated with other diseases. Anti-PR3 antibodies levels, at the moment of AAV diagnosis, correlates with disease diagnosis (specificity) and with severity but not with disease outcome. References Walker BS, et al. Autoimmun Rev. 2022 Jun;21(6):103100. Kitching AR, et al. Nat Rev Dis Primers. 2020 Aug 27;6(1):71 Image/graph:Figure 1. Receiver Operating Characteristic (ROC) plots for AAV and positive MPO-antibodies (AUC=0.7318) and disease severity at diagnosis (AUC=0.7222) Table 1. Diseases associated with positive anti-PR3 antibodies (n=54). Group Disease Number (n) Frequency (%) Vasculitis(n=44; 81.5%) Granulomatosis with polyangeiitis 33 61.1 Drug-induced vasculitis 5 9.2 Pauci-immune glomerulonephritis 2 3.7 Microscopic polyangeiitis 2 3.7 Large vessel vasculitis 1 1.9 Unclassified vasculitis 1 1.9 No vasculitis(n=10; 18.5%) Ulcerative colitis 6 11.1 Chron’s disease 1 1.9 Infection 1 1.9 Diffuse interstitial lung disease 1 1.9 Hypereosinophil syndrome 1 1.9 Acknowledgements: NIL. Disclosure of Interests Vanesa Calvo-Río Speakers bureau: AbbVie, Lilly, MSD, UCB Pharma, Grunenthal and Celgene., Salma Al Fazazi: None declared, Mónica Renuncio-García: None declared, Maria Rodriguez Vidriales: None declared, Clara Escagedo Cagigas: None declared, Juan Irure-Ventura: None declared, Luis Martín-Penagos: None declared, Alba Herrero-Morant: None declared, Marcos Lopez-Hoyos: None declared, Ricardo Blanco Speakers bureau: Abbvie, Pfizer, Roche, Bristol-Myers, Janssen, Lilly and MSD, Grant/research support from: Abbvie, MSD and Roche. Keywords: Vasculitis, Autoantibodies DOI: 10.1136/annrheumdis-2023-eular.3355Citation: , volume 82, supplement 1, year 2023, page 2078Session: Validation of outcome measures and biomarkers (Publication only)