Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

ANCA


At a Glance

Why Get Tested?

To help detect, aid in the diagnosis of, and sometimes monitor certain forms of the autoimmune disorder systemic vasculitis (inflammation of blood vessels)

To help distinguish between Crohn disease (CD) and ulcerative colitis (UC), the two most common types of inflammatory bowel disease (IBD); as an adjunct to other IBD testing

When to Get Tested?

When you have symptoms such as fever, muscle aches, and weight loss that your health practitioner thinks may be due to a vascular autoimmune disorder; sometimes to monitor response to therapy

When you have symptoms such as persistent or intermittent diarrhea and abdominal pain that your health practitioner suspects may be due to an IBD; when your health practitioner wants to distinguish between CD and UC

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

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.

ANCA may be present in several autoimmune disorders that cause inflammation, tissue damage, and organ failure:

  • 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)
  • (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 maybe seen in all three types with varying degrees of reactivity.

  • 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 atypicalANCA is generally associated with UC (80% of patients), while only 20% of CD patients may be positive.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test