The Shared Health Immunology Laboratory at St. Boniface Hospital will be changing its testing platform for MPO and PR3 antibody testing.

MPO (Myeloperoxidase) and PR3 (Proteinase 3) are crucial ANCA markers for diagnosing small-vessel vasculitis, with high titers helping to differentiate these autoimmune conditions from mimics. PR3-ANCA is strongly associated with Granulomatosis with polyangiitis, while MPO-ANCA is often linked to Microscopic Polyangiitis, aiding in prognosis, disease monitoring, and predicting relapse.

Changes in Test Procedure:

1. Testing for MPO and PR3 will be changing from an ELISA to a Chemiluminescent (CLIA) method.
2. There is no change to current reflex algorithms for IFA ANCA results. Individual MPO, PR3 or both tests are reflexed to confirm a positive/indeterminate IFA ANCA result based on the observed pattern. MPO or PR3 can also be ordered as a standalone test to monitor antibody levels in patients with established vasculitis

Test: MPO Laboratory Information Manual – MPO
Delphic Code: MPO
Delphic Labels: CLIA
Sample: Serum 1.0 ml (All CLIA tests can be performed on single 1.0ml aliquot)
Normal Range: 0.0 –20.0 AU/ml
Availability: Weekdays (3-5day TAT)
Requisition: Immunology Autoimmune Laboratory Requisition

Test: PR3 Laboratory Information Manual – PR3
Delphic Code: PR3
Delphic Labels: CLIA
Sample: Serum 1.0 ml (All CLIA tests can be performed on single 1.0ml aliquot)
Normal Range: 0.0 –24.9 AU/ml
Availability: Weekdays (3-5day TAT)
Requisition: Immunology Autoimmune Laboratory Requisition

Patient Impact:

• As no international reference serum exists for antibodies against MPO/PR3, the calibration and reporting are in arbitrary units (AU/ml). There is no linear correlation between the CLIA and ELISA methods. All patients being monitored will require rebaseline testing.
• Discrepancies observed for PR3 results may be explained by the fact that the current ELISA PR3 test kit uses a mixture of human native and human recombinant PR3 antigens while CLIA PR3 utilizes high-quality human native PR3 antigens only.

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Submitted by: Tamara Burnham, Collaborative Practice Lead