LAUSR

OBJECTIVES Anti-neutrophil cytoplasmic autoantibodies [ANCA) are important for diagnosis of ANCA-associated vasculitides (AAV). The timing of antibody development is not well established. To investigate the development of proteinase 3 (PR3)- and myeloperoxidase (MPO)-ANCA, blood samples collected before onset of symptoms of AAV were analysed. METHODS To identify AAV patients with blood samples predating symptoms, the National Patient Register and Cause of Death register were scrutinized for ICD codes for AAV and linked to the registers of five biobanks. Diagnoses of AAV and time point for symptom onset were confirmed by reviewing 504 case-record. Eighty-five AAV cases (34 males, 51 females) with samples >1 month < 10 years from AAV symptom onset and two controls matched for sex, age, and sampling time for each case were included. Samples were screened using ELISAs for ANCA and further analysed for PR3-or MPO- specificities. RESULTS In ANCA-screen 35.7% of the pre-symptomatic cases and 3.5% of controls tested positive (p < 0.01). 26.2% of the cases were PR3-ANCA+ and 10.7% MPO-ANCA+. Median (Q1-Q3) predating time for PR3-ANCA+ was 2.7 (0.3-7.7) years and MPO-ANCA+ 2.0 (0.9-3.5) years. PR3-ANCA was demonstrated in samples up to nine years before symptom onset. At symptom onset predating PR3-ANCA+ cases were younger than PR3-ANCA- (P < 0.01), and MPO-ANCA+ were older than MPO-ANCA- (p < 0.05). Predating MPO-ANCA+ cases vs. MPO-ANCA- and vs. PR3-ANCA+ cases had more often at symptoms onset manifestations from lungs, kidneys or peripheral nervous system (p < 0.01 and p < 0.05, respectively). CONCLUSION The PR3-and MPO-ANCAs are present years before AAV symptom onset and represent distinct diseases.