Proteinase 3 (PR3) Autoantibodies as a Serological Marker in Inflammatory Bowel Disease (IBD)

Abstract

Purpose: Autoantibodies to proteinase 3 (PR3) have recently been shown to be a biomarker of ulcerative colitis (UC) when tested by a novel chemiluminescence assay (CIA). The objective of this study was to determine if anti-PR3 by CIA differentiates UC from Crohn's disease (CD) in a large cohort of IBD patients. Methods: Four hundred twenty five patients (333 CD, 92 UC) from the Alberta Innovates - Health Solutions (AIHS) Alberta IBD Consortium were tested by QUANTA Flash® PR3 on BIO-FLASH® CIA (INOVA Diagnostics, San Diego, CA), QUANTA Lite® PR3 ELISA (INOVA Diagnostics Inc.), and indirect immunofluorescence (IIF) on formalin and ethanol-fixed neutrophil substrates for anti-neutrophil cytoplasmic antibodies (ANCA: INOVA Diagnostics Inc). Statistical evaluation was performed using Analyse-it software (Version 2.03; Analyse-it Software, Ltd., Leeds, UK). Mann-Whitney U-test was used to analyze differences between groups, and Fisher's exact test to qualitatively compare groups. P values <0.05 were considered significant. Results: By CIA, 29/92 (31.5%) patients with UC were positive for PR3, compared to 39/333 (11.7%) CD patients (p<0.0001). Mean titers were 28.2 chemiluminescent units (CU) (95% CI 16.7-39.7) in UC, and 13.5 CU (95% CI 8.5-18.4) in CD (p=3.0x10-13). By ELISA, only 14/92 (15.2%) UC patients and 15/333 (4.5%) CD patients were positive for PR3 (p=0.0018). Atypical ANCA (aANCA), a known marker for UC, was observed in 10/92 (10.8%) of UC, and 8/333 (2.4%) of CD (p=0.0001). Clinical sensitivities and specificities were comparable between the assays (Table 1). The manufacturer's recommended cut-off value is 20 CU; however, using a value of 92 CU increased the specificity.Table 1: Comparison of diagnostic performance of different assays for UCConclusion: In the setting of serological analysis of IBD, PR3 is a specific marker for UC, and has higher titers compared to CD. PR3 measured by CIA detected more patients than ELISA. CIA provides advantages for the diagnostic laboratory because it avoids the limitations of IIF on ANCA, as it is less dependent on subjective interpretation and has a rapid (30 minute) turnaround time. Disclosure - Dr. L. Stinton - Consultant: INOVA Diagnostics Inc; Dr. M. Mahler - Employee, INOVA Diagnositcs Inc.; Dr. M. Fritzler - Consultant: INOVA Diagnostics Inc.