Myeloperoxidase (MPO) enzyme is found in primary granules of neutrophil and monocyte lysosomes. Autoantibodies related to MPO (MPO antineutrophil cytoplasmic antibodies, i.e, ANCA) occur in several diseases and may be related to the pathogenesis of vascular inflammation in patients having microscopic polyangiitis (MPA).Patients with MPA often experience MPO ANCA and may also found with azotemia which is secondary to glomerulonephritis (pauci-immune necrotizing glomerulonephritis).MPO ANCA can also be seen in patients with:
1. Systemic lupus erythematosus(with or without lupus nephritis)
2. Goodpasture syndrome.
3. Churg-Strauss syndrome.