Anti-myeloperoxidase and proteinase 3 antibodies for nephritis flare prediction in anti-neutrophil cytoplasmic antibody–associated vasculitis.

Background The value of myeloperoxidase (MPO) and proteinase 3 (PR3) antibody titres in the assessment of renal disease activity and flare prediction in patients with anti-neutrophil cytoplasmic antibody–associated vasculitis (AAV) is not well known. Methods We performed a retrospective study including 113 AVV patients with renal biopsy–proven pauci-immune necrotizing glomerulonephritis from seven Spanish hospitals. The main inclusion criteria were assessment of MPO antibodies using multiplex flow immunoassay and PR3 antibody measurements using immunoassay chemiluminescence with an identical range of values for all participating centres. Results Serum MPO antibodies 3 ± 1.2 months before relapse were higher in patients who relapsed [19.2 ± 12.2 versus 3.2 ± 5.1 antibody index (AI); P < 0.001]. The discrimination value of MPO antibodies 3 months before renal relapse had an area under the receiver operating characteristics curve (AUC) of 0.82 [95% confidence interval (CI) 0.73–0.92; P < 0.001]. ΔMPO antibodies (change in antibodies titration 6 months before relapse) were higher in patients who relapsed (8.3 ± 12 versus 0.9 ± 3.1 AI; P = 0.001). The discrimination value of ΔMPO had an AUC of 0.76 (95% CI 0.63–0.88; P < 0.001). The positive predictive value of renal relapse in PR3 patients is 100% and the negative predictive value of renal relapse in patients with PR3-positive titres is 57.1%. Serum PR3 antibodies were higher in patients who relapsed 2.8 ± 1.4 months before relapse (58.6 ± 24.6 versus 2.0 ± 0.6 AI; P < 0.001). Conclusions MPO level monitoring using multiplex flow immunoassay and PR3 measurements using immunoassay chemiluminescence are useful and sensitive tools for the prediction of renal relapse in the follow-up of AAV patients with renal disease and relevant surrogate markers of renal disease activity. [ABSTRACT FROM AUTHOR]