ANCA test has no value in subtyping IBD

ANCA (anti-neutrophil cytoplasmic antibody) tests do not help discriminate Crohn’s disease from ulcerative colitis, results from an Australian IBD clinic suggest.

A retrospective review of ANCA tests results for 64 patients treated at the Canberra Hospital also found that positivity for the PR3 was common but did not have value in predicting systemic vasculitis.

The study found that ANCA tests showed unusually high rates of positivity (86%) and there was little correlation with the type of IBD.

Of the 40 patients with Crohn’s disease, 33 (83%) were positive by either IIF or for MPO/PR3. Of the 21 patients with ulcerative colitis, 19 (90%) were positive by IIF or for MPO/PR3.

The study investigators said the most striking finding from their review was the high rate of positivity for PR3 ANCA (20 of 64 patients). However PR3 positivity did not predict a specific IBD subtype or clinical course of IBD.

Of the PR3 positive IBD patients, 11 (55%) had CD, seven (35%) had UC, and two (10%) had indeterminate colitis. This was similar to the distribution of IBD subtypes amongst double negative patients.

The finding of a positive PR3 ANCA may cause concern for both the clinician and patient due to the association with systemic vasculitis, the study authors noted.

“Identifying MPO or PR3 antibodies in patients with IBD may lead to a battery of investigations in an effort to exclude systemic vasculitis because ANCA vasculitis and IBD can co-exist on very rare occasions.

“Reassuringly none of the patients in our study had diagnosed concurrent systemic vasculitis, and our study suggests that in IBD a positive PR3 result is unlikely to indicate systemic vasculitis.

The study investigators acknowledged the limitations of data from a retrospective non-randomised study.

“However, despite this our data indicate that in a tertiary hospital IBD clinic there is little clinical value in ordering an ANCA test to evaluate for subtypes of IBD,” they wrote.

“t also suggests that patients who are PR3 ANCA positive without evidence of systemic vasculitis may have IBD.”

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