Background/Purpose: Anti-neutrophil cytoplasmic antibodies (ANCA) are a hallmark of a subset of small vasculitides collectively termed ANCA-associated vasculitis (AAV). With widespread availability of ANCA testing, interpreting positive results has become increasingly challenging. Here, we conducted a retrospective study to evaluate indications for testing and diagnosis of patients with positive ANCA.

Methods: We searched The Ottawa Hospital biochemistry database and reviewed the records of patients with positive ANCA (defined as elevated myeloperoxidase [MPO] or proteinase 3 [PR3] titers) tested between April 1, 2014 and March 31, 2015. Indications for ordering ANCA and final diagnosis were determined.

Results: 1889 ANCA tests were performed in the study year. 112 patients had at least 1 positive ANCA in the study year and 169 total tests were positive. Indications and diagnosis of patients with first-time positive ANCA testing: 69 patients had first-time positive ANCA in the study year, with 35 (51%) anti-MPO positive, 31 (45%) anti-PR3 positive, and 3 (4%) doubly positive. The indications for testing were suspicion for AAV in 20 patients (29%), suspicion for unspecified vasculitis in 20 (29%), suspicion for an inflammatory condition in 25 (36%), and unknown in 4 (6%). Overall, 27 patients (39% of first time positives) were diagnosed with AAV corresponding to 80%, 40%, 12%, and 0% of patients tested for these indications, respectively. Thirty-one (45%) patients had other inflammatory or infectious etiologies (most commonly inflammatory bowel disease (n=5), lupus (n=4), and inflammatory eye diseases (n=3)), and non-inflammatory diagnoses accounted for the remaining 11 (16%). Patients with AAV had significantly higher mean maximum PR3 and MPO titers than those with non-AAV diagnoses (1138 vs. 145 and 323 vs. 119 respectively, p<0.05 by Student’s t-test). Indications and outcomes of repeat ANCA testing: 68 patients had repeat ANCA testing in the study year, 43 of which were first tested prior to the study year. In total, 120 repeat ANCAs were performed; 84 of these were done on 44 patients with AAV and 36 on 24 patients with other diagnoses. Altogether, 80% of patients with AAV were re-tested in the study year (between 1 and 6 times, median 2 tests) vs. 42% of those with non-AAV conditions (between 1 and 5 times, median 1 test). Routine monitoring (as opposed to testing for changed clinical status) accounted for 72% of all repeat tests (n=86). Management was changed in response to serial ANCA testing in 11 AAV patients, 10 of whom were tested at time of changed clinical status. Overall, management was changed in 9% of all patients with repeat ANCA, 34% of all re-tests performed for changed clinical status and 1% of re-tests conducted routinely.

Conclusion: Despite widespread ANCA testing, few patients who start with low clinical suspicion for AAV and have positive ANCA are subsequently diagnosed with AAV. Serial ANCA testing is a common practice but is not supported by clear evidence, and few ANCA re-tests subsequently lead to change in management. Clarification of guidelines on effective ANCA ordering may limit unnecessary hospital laboratory costs and patient bother.

« Back to 2016 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/indications-for-testing-and-diagnostic-outcome-in-patients-with-positive-anca-at-a-canadian-tertiary-care-centre/