Table 4.

Temporal relationship between surpassed PR3-ANCA thresholds and elevated CRP levels in GPA patients

PR3 Antibody (U/ml)	Before CRP (>0.8 mg/dl) (%)	After CRP (>0.8 mg/dl) (%)	Odds Ratio	95% Confidence Interval	P Value (Fisher’s Exact)
>/6	67 (12/18)	33 (6/18)	4.0	1.0 to 16	0.04
>2	80 (16/20)	20 (4/20)	16	3.4 to 75	<0.001
>1	86 (18/21)	14 (3/21)	36	6.4 to 203	<0.001
>0	96 (23/24)	4 (1/24)	529	31.2 to 8977	<0.001

Antecedent increase in PR3-ANCA or CRP was established for patients with a serum sample that had only one biomarker above the designated threshold value. If both became elevated in the same sample or if neither was elevated in any sample, there was no antecedent elevation determined. Because subclinical PR3-ANCA levels above the threshold of 0 U/ml, 1 U/ml, and 2 U/ml within the normal clinical range were associated with future GPA, we also compared the percentage of GPA patients with an antecedent antibody above these thresholds to the percentage of patients that first had an elevated CRP. PR3, proteinase-3; GPA, granulomatosis with polyangiitis; CRP, C-reactive protein.