Test Id : MPO

To distinguish between microscopic polyangiitis and other forms of anti-neutrophil cytoplasmic antibody-associated vasculitis, also order PR3 / Proteinase 3 Antibodies, IgG, Serum and ANCA / Cytoplasmic Neutrophil Antibodies, Serum; alternatively, VASC / Antineutrophil Cytoplasmic Antibodies Vasculitis Panel, Serum may be ordered instead, which initially tests for myeloperoxidase and proteinase 3 antibodies, with reflex to ANCA when appropriate.

Supplies: Sarstedt Aliquot Tube 5 mL (T914)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

0.35 mL

Evaluating patients with clinical features anti-neutrophil cytoplasmic antibody associated vasculitis, specifically granulomatosis with polyangiitis, microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis

Distinguishing between MPA and other forms of ANCA-associated vasculitis, in conjunction with proteinase 3 antibody and cytoplasmic neutrophil antibody testing

Following treatment response or monitoring disease activity in patients with myeloperoxidase (MPO) antibodies

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides are characterized by a pauci-immune inflammation within the walls of small blood vessels.(1) There are 3 specific diseases which are identified as ANCA-associated vasculitides: microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA), and eosinophilic granulomatosis with polyangiitis (EGPA). The serological hallmark of these disorders is the presence of ANCA, which are antibodies that bind to cytoplasmic antigens found in the granules of neutrophils.(2) Patients with GPA frequently have antibodies specific for proteinase 3 (PR3), while individuals with MPA or EGPA are more likely to have antibodies that bind to myeloperoxidase (MPO). The presence of PR3-ANCA and MPO-ANCA can be detected using antigen-specific immunoassays or indirect immunofluorescence (IIF). IIF is typically performed using ethanol-fixed neutrophils. Using this substrate, anti-PR3 antibodies produce a granular cytoplasmic staining pattern, which is referred to as cANCA. In comparison, due to an artefact that is a result of the fixation process, anti-MPO antibodies display a perinuclear pattern (pANCA).

Patients with suspected ANCA-associated vasculitis should be evaluated for the presence of PR3-ANCA, MPO-ANCA and ANCA by IIF. A consensus guideline published in 2017 recommends that patients with possible GPA or MPA be tested for PR3-ANCA and MPO-ANCA using antigen-specific immunoassays.(3) ANCA by IIF should then be used in cases where there is a high degree of suspicion for GPA or MPA, but the PR3-ANCA and MPO-ANCA testing is negative. To improve specificity of the testing, this guideline also suggests that ANCA be used in situations where a low-positive PR3-ANCA or MPO-ANCA level is detected. The classification criteria for MPA, GPA, and EGPA published by the American College of Rheumatology and the European Alliance of Associations for Rheumatology include PR3-ANCA and MPO-ANCA detected by either antigen-specific immunoassay or IIF.(4-6) These classification criteria incorporate serological ANCA testing along with clinical symptoms, imaging, and biopsy results to determine a score that allows for the classification of the various ANCA-associated vasculitides.

<0.4 U (negative)

0.4-0.9 U (equivocal)

> or =1.0 U (positive)

Reference values apply to all ages.

Positive results for myeloperoxidase (MPO)-antineutrophil cytoplasmic antibodies (ANCA) by antigen-specific immunoassay and perinuclear ANCA by indirect immunofluorescence are consistent with the diagnosis of microscopic polyangiitis (MPA) or eosinophilic granulomatosis with polyangiitis, in patients with the appropriate clinical presentation.

The reactivity of MPO-ANCA may decline with treatment of patients with MPA.

A positive result for proteinase 3 (PR3)-anti-neutrophil cytoplasmic antibodies (ANCA), myeloperoxidase (MPO)-ANCA, or ANCA by indirect immunofluorescence (IIF) is not diagnostic for any ANCA-associated vasculitis and must be interpreted in the clinical context of the patient.

Negative results for PR3-ANCA, MPO ANCA, and ANCA by IIF do not exclude the possibility of ANCA-associated vasculitis.

Monitoring reactivity of PR3-ANCA or MPO-ANCA should not be relied upon exclusively to evaluate response to treatment or to assess for risk of disease flare.

1. Kitching AR, Anders HJ, Basu N, et al. ANCA-associated vasculitis. Nat Rev Dis Primers. 2020;6(1):71

2. Ramponi G, Folci M, De Santis M, et al. The biology, pathogenetic role, clinical implications, and open issues of serum anti-neutrophil cytoplasmic antibodies. Autoimmun Rev. 2021;20(3):102759

3. Bossuyt X, Cohen Tervaert W, Arimura Y, et al. Revised 2017 international consensus on testing of ANCAs in granulomatosis with polyangiitis and microscopic polyangiitis. Nat Rev Rheumatol. 2017;13(11):683-692

4. Suppiah R, Robson JC, Grayson PC, et al. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for microscopic polyangiitis. Ann Rheum Dis. 2022;81(3):321-326. doi:10.1136/annrheumdis-2021-221796

5. Robson JC, Grayson PC, Ponte C, et al. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for granulomatosis with polyangiitis. Ann Rheum Dis. 2022;81(3):315-320. doi:10.1136/annrheumdis-2021-221795

6. Grayson PC, Ponte C, Suppiah R, et al. 2022 American College of Rheumatology/European Alliance of Associations for Rheumatology classification criteria for eosinophilic granulomatosis with polyangiitis. Ann Rheum Dis. 2022;81(3):309-314. doi:10.1136/annrheumdis-2021-221794

Myeloperoxidase (MPO) antigen is covalently coupled to polystyrene microspheres that are impregnated with fluorescent dyes to create a unique fluorescent signature. MPO antibodies, if present in diluted serum, bind to the MPO antigen on the microspheres. The microspheres are washed to remove extraneous serum proteins. Phycoerythrin (PE)-conjugated antihuman IgG antibody is then added to detect anti-MPO IgG bound to the microspheres. The microspheres are washed to remove unbound conjugate, and bound conjugate is detected by laser photometry. A primary laser reveals the fluorescent signature of each microsphere to distinguish it from microspheres that are labeled with other antigens. A secondary laser reveals the level of PE fluorescence associated with each microsphere. Results are calculated by comparing the median fluorescence response for MPO microspheres to a 4-point calibration curve.(Package insert: Bio-Plex 2200 Vasculitis. Bio-Rad Laboratories; 02/2018)

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This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

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