Anti-myeloperoxidase antibodies (Anti-MPO)

The test is used to diagnose systemic ANCA-associated vasculitis and rapidly progressive glomerulonephritis. Antibodies to myeloperoxidase represent a type of antineutrophil cytoplasmic antibody (ANCA). Unlike proteinase 3 antibodies, myeloperoxidase antibodies are not highly specific for the diagnosis of any particular vasculitis but can be detected in all ANCA-associated vasculitis and related diseases.

Antibodies to myeloperoxidase are found in most patients with idiopathic necrotizing vasculitis with demilunes, microscopic polyangiitis, Churg-Strauss syndrome, and Wegener's granulomatosis without antibodies against proteinase 3. Antibodies to myeloperoxidase may be noted in Goodpasture's syndrome. Although the detection of antineutrophil antibodies is highly specific to systemic vasculitis, they may occur in infectious, paraneoplastic, and drug-induced vasculitis.

Antibodies to myeloperoxidase may rarely occur in lupus nephritis. The predominant form of vasculitis in patients with antibodies to myeloperoxidase is microscopic polyangiitis, which affects small-caliber vessels and clinically manifests with combined pulmonary and renal involvement. In addition, approximately one-third of patients with antibodies to myeloperoxidase have rapidly progressive glomerulonephritis with demilunes that is not accompanied by extrarenal manifestations.

Levels of antibodies to myeloperoxidase are maximal during active glomerulonephritis. Quiescence of the process or suppression of vasculitis activity with effective cytostatic therapy leads to elimination of antibodies in 95% of patients, and in 75% of patients seroconversion occurs within the next 6 months after achieving clinical remission of the process. Another frequent clinical form of granulomatous vasculitis that is accompanied by antibodies to myeloperoxidase is Churg-Strauss syndrome. The clinical symptomatology of this disease is represented by pulmonary vasculitis with eosinophilic infiltrates, asthma and hypereosinophilia.

Antibodies to myeloperoxidase in Churg-Strauss syndrome are detected in 40-70% of patients