217. Does introducing a gating policy for ANCA testing result in delayed diagnosis of ANCA-associated Vasculitis?
Creators: name: McDermott1, Rachel
name: Wall1, Karena
name: Nelson1, Judith
name: Onn1, Frankie Ngieng Hui
name: Clooney1, Anne
name: Keogan1, Mary
name: Khairin  Khalib1
Publisher: name: Zenodo
Year: 2022
Subjects: Vasculitis
ANCA
Abstracts
Giant Cell Arthritis
MPA
GPA
EGPA
Takayasu
IgA vasculitis

description: <strong>Background: </strong>ANCA are markers for well-defined types of small-vessel vasculitis. Most diagnostic laboratories test for ANCA by indirect immunofluorescence (IIF), with reflex testing of IIF positives by immunoassay for anti-PR3 and anti- MPO. The 2017 revision of the 1999 international consensus on ANCA testing in GPA and MPA concluded that immunoassays can be used as the primary method for ANCA testing, without the categorical need for IIF and recommended that a gating policy based on clinical indications be used to limit requests for ANCA testing. Potential unintended consequences include delayed diagnosis of vasculitis for cases where gating criteria are not met, loss of essential IIF skills in laboratories, and well as cost. Our laboratory uses an IIF method validated to have a 100% sensitivity for detection of anti-MPO and anti-PR3 with reflex immunoassay testing of IIF positive samples, and we assessed the potential impact of the 2017 revised consensus. The aims of this audit were to confirm the sensitivity of IIF screening, determine compliance of requests with 2017 gating criteria, and determine if all patients diagnosed with ANCA-associated vasculitis (AAV) would have met gating criteria at the time of diagnosis. <strong>Methods: </strong>We tested 250 consecutive serum samples that were negative for ANCA by IIF by immunoassay for PR3 and MPO, and assessed concordance. Indications for testing, where available were reviewed and compared with the gating criteria. We identified all positive PR3 and MPO samples over the past 4 years, assessed the indication for ANCA testing by reviewing medical records and compared the indication with the gating policy in the 2017 consensus. We assessed how many ANCA positive patients were ultimately diagnosed with AAV. <strong>Results: </strong>All 250 IIF negative samples tested negative for both MPO and PR3 by ELISA. The clinical indication for 127 of these requests from Beaumont Hospital were available, of which 40 fitted the 2017 gating policy and 87/127 did not. Of 16,958 samples tested for ANCA, between 01/01/2017 to the 31/12/2020, 1,974 (11.6%) were tested for anti-MPO/PR3. 70 new patients were identified (0.4% of total tested; 3.5% of those tested for anti-MPO/PR3). 29 with positive for anti- MPO (Range 3.5 - &gt;134 U; Ref &lt; 3.5U); 38 for anti- PR3 (Range 2.1 – 150U; Ref &lt;2.0U). 3 were dual positive. Indications for testing 33 (47%) patients fitted the gating policy while 37 (53%) did not. 16 patients were diagnosed with AAV; 6 MPO-associated Vasculitis, 7 PR3-associated vasculitis, 1 dual positivity (drug induced) and 2 Eosinophilic granulomatosis with polyangiitis (EGPA), both MPO positive. Of the 16 patients diagnosed with vasculitis, 13 (81%) fitted the gating policy clinical indications while 3 (19%) did not. <strong>Conclusions:</strong> This audit demonstrates that initial testing for ANCA with an IIF method with validated sensitivity is not inferior to testing all samples with immunoassays. A sampling exercise showed that 63% of requests for ANCA testing in our centre do not fulfil the clinical indication suggested in the 2017 Consensus. Samples fulfilling the gating criteria accounted for 47% of ANCA positive samples, and 81% of patients ultimately diagnosed with AAV. Use of gating criteria would have delayed diagnosis for 19% of patients with AAV. <strong>Disclosures: </strong>None