The Test Sample
What is being tested?
Antineutrophil cytoplasmic antibodies (ANCA) are autoantibodies produced by a person's immune system that mistakenly target and attack proteins within the person's neutrophils (a type of white blood cell). ANCA testing detects and measures the amount of these autoantibodies in the blood. Two of the most common types or subsets of ANCA are the autoantibodies that target the proteins myeloperoxidase (MPO) and proteinase 3 (PR3).
For the test, an individual's blood sample is mixed with neutrophils and the mixture is placed on a slide and treated with a fluorescent stain. If ANCA are present, they will produce a pattern of fluorescence that can be seen under a microscope. The pattern may be identified as cytoplasmic or cANCA, perinuclear (pANCA), or atypical ANCA (X-ANCA). Alternatively, the laboratory may test for myeloperoxidase antibodies or proteinase 3 antibodies directly using an ELISA assay. A combination of both fluorescence and ELISA tests are often done when working up suspected cases of vasculitis.
- Systemic vasculitis is a group of disorders associated with damage and weakening of blood vessels. It can cause tissue and organ damage due to the narrowing and obstruction of blood vessels and the subsequent loss of blood supply. It can also produce areas of weakness in blood vessel walls, known as aneurysms, which have the potential to rupture. The symptoms experienced by a person with systemic vasculitis depend upon the degree of autoimmune activity and the parts of the body involved. A few types of systemic vasculitis are closely associated with the production of ANCA:
- Granulomatosis with polyangiitis (Wegener granulomatosis)
- Microscopic polyangiitis
- Eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome)
- Polyarteritis nodosa (PAN)
- Ulcerative colitis (UC) is a type of inflammatory bowel disease (IBD) associated with swollen and damaged tissues in the lining of the colon. UC can be difficult to distinguish from Crohn disease (CD), another type of IBD that can affect any part of the intestinal tract. The presence of atypical ANCA is generally associated with UC (80% of patients), while only 20% of CD patients may be positive.
(For more information on these specific conditions, see the article on Vasculitis).
cANCA/PR3 antibodies are most frequently seen in granulomatosis with polyangiitis and pANCA/ MPO antibodies are most often associated with microscopic polyangiitis. However, both may be seen in all three types with varying degrees of reactivity.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.