Table 1.

IgA and IgG isotypes of anti-PR3 antibodies are present in patients with GPA

	Controls	WGGER	VCRC
IgA positive only	1 (1%)	12 (3.6%)	45 (17.1%)
IgG positive only	1 (1%)	151 (45.1%)	80 (30.4%)
IgA and IgG positive	0 (0%)	49 (14.6%)	56 (21.3%)
Negative	97 (98%)	123 (36.7%)	82 (31.2%)
Total	99	335	263

Data were obtained by ELISA. Of the 463 Caucasian patients with GPA in WGGER, 335 had single samples available. Patients from the VCRC cohort typically contributed multiple samples (263 participants, 1,470 samples), and a patient was counted as positive if any sample tested positive. Healthy controls were assayed to determine a threshold for positivity, as described in Methods.