Myeloperoxidase (MPO) antibody assay is used to evaluate patients with suspected vascular immunological etiology, mainly microscopic polyangiitis, and to monitor disease activity and response to treatment in patients with microscopic polyangiitis.
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The ANCA antibodies (AntiNeutrophil Cytoplasmic Antibody) 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 helpful in monitoring the disease's progression, 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 are crucial in diagnosing Wegener's granulomatosis and other systemic vasculitis syndromes.
When ANCA antibodies are detected by indirect immunofluorescence microscopy, two major staining patterns 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. They also occur in patients with glomerulonephritis other than Wegener's granulomatosis, such as 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's granulomatosis, microscopic polyarteritis, idiopathic rapidly progressive glomerulonephritis, ulcerative colitis, primary sclerosing cholangitis, autoimmune hepatitis, Churg-Strauss vasculitis, active viral hepatitis, Crohn's disease
Important Note
Laboratory test results are crucial for diagnosing and monitoring all pathological conditions. Between 70 to 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 analyzed based on each case and family history, clinical findings, and other laboratory tests and information. Your physician should explain the importance of your test results.
At Diagnostiki Athinon, we answer any questions you may have about the test you perform in our laboratory and contact your doctor to ensure you receive the best possible medical care.
