Relation between asymptomatic proteinase 3 antibodies and future granulomatosis with polyangiitis.

BACKGROUND AND OBJECTIVES The subclinical pathogenesis of granulomatosis with polyangiitis (GPA) has not been completely elucidated. Proteinase 3 (PR3) antibodies are strongly associated with GPA, but have not been evaluated before disease presentation. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS This was a retrospective case-control serum bank study in which PR3 antibodies and C-reactive protein (CRP) in up to three longitudinal serum samples for 27 GPA patients before diagnosis (1 day-19 years) were compared with 27 controls whose serum samples were matched for age, sex, and race. This study analyzed all patients with American College of Rheumatology criteria-confirmed disease identified in the Department of Defense electronic medical records between 1990 and 2008. RESULTS A greater percentage of GPA patients had at least one elevated PR3 antibody level (≥6 U/ml) as well as at least one detectable PR3 antibody level (>1 U/ml) before diagnosis compared with matching controls (63% [17 of 27] versus 0% [0 of 27], P<0.001; and 85% [23 of 27] versus 4% [1 of 27], P<0.001, respectively). A greater percentage of GPA patients had a >1 U/ml per year rate of increase in PR3 antibody level compared with matching controls (62% [21 of 26] versus 0% [0 of 26], P<0.001). PR3 antibody more frequently became elevated before CRP (67% [12 of 18] versus 33% [6 of 18], P=0.04). CONCLUSIONS Subclinical PR3 antibody presence, trajectory, and temporal relationship to CRP associates with the future diagnosis of GPA. This data set further elucidates the pathogenesis of GPA.