AB1681 ARE PR3 ANTIBODY TITERS REALLY IMPORTANT FOR ROUTINE CLINICAL PRACTICE?. STUDY FROM A SINGLE UNIVERSITY HOSPITAL

Abstract

BackgroundAnti-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].ObjectivesIn 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.MethodsObservational 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.ResultsWe 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%).Table1 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).ConclusionThe 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.