Myeloperoxidase antibodies

Myeloperoxidase Antibodies, IgG, Serum

Useful in evaluating patients suspected of having immune-mediated vasculitis, especially microscopic polyangiitis (MPA), when used in conjunction with other autoantibody tests.

May be useful to follow treatment response or to monitor disease activity in patients with microscopic polyangiitis.

Myeloperoxidase (MPO) enzyme is found in neutrophil primary granules and monocyte lysosomes.

Myeloperoxidase catalyzes the conversion of hydrogen peroxide to hypochlorite and hypochlorous acid, and is encoded by a single gene that undergoes posttranslational modification to produce the active enzyme found in leukocytes.

Autoantibodies to MPO (MPO antineutrophil cytoplasmic antibodies: ANCA) occur in several diseases and may be involved in the pathogenesis of vascular inflammation in patients with microscopic polyangiitis (MPA).

Patients with MPA often develop MPO ANCA and may present with azotemia secondary to glomerulonephritis.

MPO ANCA are not specific for MPA, and also may be detected in patients with systemic lupus erythematosus with or without lupus nephritis, Goodpasture syndrome and Churg-Strauss syndrome.

Lupus nephritis and Goodpasture syndrome, as well as Wegener granulomatosis may present with azotemia and progressive renal failure.

Myeloperoxidase antibodies

<0.4 U (negative)

0.4-0.9 U (equivocal)

> or =1.0 U (positive)

A positive result has a high predictive value for microscopic polyangiitis in patients with negative test results for systemic lupus erythematosus (antinuclear antibodies) and Goodpasture syndrome (glomerular basement membrane antibody).

A negative result significantly diminishes the likelihood that a patient has MPA.

It is not possible to distinguish between microscopic polyangiitis (MPA) and other causes of progressive renal failure or systemic illness such as Wegener granulomatosis, lupus nephritis, Goodpasture syndrome.

The test for ANCA identifies 2 types of antibodies-cytoplasmic (cANCA), which are specific for PR3 and perinuclear (pANCA), which are specific for MPO.

The presence of MPO is quite specific for MPA with a diagnostic specificity approaching 95%.

pANCA, confirms the positive MPO result and increases the diagnostic specificity for MPA to 97%.

Positive results for MPO have been reported in patients with systemic lupus erythematosus, Goodpasture syndrome, and Churg-Strauss syndrome, so it is necessary to rule out these diagnoses to maximize the specificity and positive predictive value of the MPO test result.

Sequential measurements of MPO may be used to follow treatment response or to monitor disease activity in patients with MPA, results should not be exclusively relied upon to assess response to treatment or disease activity.

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