Myeloperoxidase (MPO) antibody assay is used to evaluate patients with suspected vascular immunological etiology, especially microscopic polyangiitis, as well as to monitor disease activity and response to treatment in patients with microscopic polyangiitis.
The ANCA antibodies (AntiNeutrophil Cytplasmic Antibody, Antibodies against Hydrophilic Cytoplasm) are directed against the cytoplasmic components of neutrophil granulocytes. This test is used to help diagnose granulomatous vascular diseases, such as Wegener's granulomatosis. The test is also useful in monitoring the progression of the disease, monitoring the response to treatment and early detection of relapses. Wegener's granulomatosis is a systemic peripheral vasculitis in which the small arteries of the kidneys, lungs and upper respiratory tract (nasopharynx) suffer damage from the development of granulomatous inflammation. The diagnosis is confirmed by a biopsy of the tissue presenting the clinical symptoms. Serological tests play a key role in the diagnosis of Wegener's granulomatosis and other systemic vasculitis syndromes.
When ANCA antibodies are detected by indirect immunofluorescence microscopy, two major patterns of staining are observed: cytoplasmic ANCA (c-ANCA) and perinuclear ANCA (p-ANCA). Specific immunochemical methods demonstrate that c-ANCA mainly consists of antibodies against proteinase 3 (PR3) and p-ANCA consists of antibodies against myeloperoxidase (MPO). By using antigen-specific immunochemical tests to characterize ANCA (and not standard immunofluorescence microscopy), they become more specific and sensitive to the detection of vasculitis.
Autoantibodies against Proteinase 3 Antigen (PR3) are highly specific (95% to 99%) for Wegener's granulomatosis. When the disease is restricted to the respiratory tract, antibodies against PR3 are positive in 65% of patients. Almost all patients with kidney-restricted Wegener's granulomatosis do not have positive PR3 antibodies. When Wegener's granulomatosis is inactive, the percentage of positive PR3 antibodies drops to 30%.
Autoantibodies against myeloperoxidase antigen (MPO) are found in 50% of patients with kidney-centered Wegener granulomatosis. It also occurs in patients with glomerulonephritis other than Wegener's granulomatosis, such as in microscopic polyangiitis (MPA). The p-ANCA antibodies can also be used to differentiate different forms of inflammatory bowel disease. P-ANCA antibodies were found in 50 to 70% of patients with ulcerative colitis (UC), but only in 20% of patients with Crohn's disease (CD).
Possible Interpretations of Pathological Values
- Increase: Wegener granulomatosis, microscopic polyarthritis, idiopathic rapidly evolving glomerulonephritis, ulcerative colitis, primary sclerosing cholangitis, autoimmune hepatitis, active angiitis churgitis
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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