Tests for antineutrophil cytoplasmic antibodies (ANCA) may be used to:

• Help detect and diagnose certain forms of autoimmune vasculitis, including granulomatosis with polyangiitis (Wegener granulomatosis), microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome). Sometimes this test may also be used to monitor treatment and/or detect a relapse of these conditions.(For more detailed information on these conditions, see the article on Vasculitis.)
• Help distinguish between ulcerative colitis (UC) and Crohn disease (CD), two common types of inflammatory bowel disease (IBD).

ANCA are autoantibodies produced by a person's immune system that mistakenly attack proteins within the person's neutrophils (white blood cell types). The most common subsets of ANCA are those that target the proteins myeloperoxidase (MPO) and proteinase 3 (PR3).

Two types of tests may be used:

• Most often, ANCA tests are performed using indirect immunofluorescence microscopy (IFA). Serum samples are mixed with neutrophils to allow autoantibodies that may be present to react with the cells. The sample is put on a slide and treated with a fluorescent stain. The slide is then examined under a microscope and the resulting pattern noted. The cytoplasmic pattern (cANCA) is associated with PR3 antibodies and the perinuclear pattern (pANCA) is associated with MPO antibodies. Another possible pattern is atypical ANCA.
• Myeloperoxidase antibodies and proteinase 3 (PR3) antibodies may be individually and specifically tested using an immunoassay method.

Some laboratories will perform all three tests, ANCA, MPO and PR3, as a panel while others will perform MPO and PR3 only if an initial ANCA test is positive.

Additional tests that may be performed to aid in diagnosis include erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) to check for inflammation, complete blood count (CBC) to measure and evaluate white and red blood cells, and urinalysis, blood urea nitrogen (BUN), and creatinine to evaluate kidney function. For some patients, viral studies for hepatitis or cytomegalovirus may be ordered.

Vasculitis
An ANCA test and/or tests for MPO and PR3 are ordered when a person has signs and symptoms that suggest systemic autoimmune vasculitis. Early in the disease, symptoms may be vague or nonspecific, such as fever, fatigue, weight loss, muscle and/or joint aches, and night sweats. As the disease progresses, damage to blood vessels throughout the body may cause signs and symptoms associated with complications involving various tissues and organs. A few examples include:

• Eyes — red, itchy eyes or "pink eye" (conjunctivitis); problems with sight (blurry vision, loss of vision)
• Ears — hearing loss
• Nose — runny nose or other upper respiratory symptoms that do not go away
• Skin — rashes and/or granulomas
• Lungs — cough and/or difficulty breathing
• Kidneys —protein in the urine (proteinuria)

Testing may also be performed periodically to monitor a person who has been diagnosed with an autoimmune vasculitis.

Inflammatory Bowel Disease
An ANCA test may be ordered with a test forantibodies (ASCA)Saccharomyces cerevisiaeanti- when a person has signs and symptoms that suggest inflammatory bowel disease and the health practitioner is attempting to distinguish between Crohn disease and ulcerative colitis.

Symptoms of an IBD may include:

• Abdominal pain and cramps
• Diarrhea
• Rectal bleeding
• Fever
• Fatigue
• In some people, joint, skin, bone, and organ-related symptoms
• Children may also have delayed development and growth retardation.

Results of ANCA tests must be interpreted carefully, taking several factors into account. A health practitioner will consider clinical signs and symptoms in addition to results of the laboratory tests and other types of tests, such as imaging studies.

Vasculitis

Positive ANCA, PR3, and/or MPO tests help to support a diagnosis of systemic autoimmune vasculitis and to distinguish between different types. However, to confirm a diagnosis, a biopsy of an affected site is often required.

Negative ANCA tests results mean it is unlikely that a person's symptoms are due to an autoimmune vasculitis.

For a positive result on the indirect immunofluorescence microscopy method, several different ANCA patterns may be seen:

• Perinuclear (pANCA) – most of the fluorescence occurs near the nucleus. About 90% of samples with a pANCA pattern will have MPO antibodies.
• Cytoplasmic (cANCA) – the fluorescence occurs throughout the cytoplasm of the cell. About 85% of samples with a cANCA pattern will have PR3 antibodies.
• Negative ANCA — very little or no fluorescence

If an ANCA test result is positive, then an additional test is performed to determine the amount of antibody present. This is called a titer. To determine the titer, a serum sample is diluted in steps and each dilution is tested for the presence of the antibody. The greatest dilution at which the antibody can be detected is the titer. For example, if a serum tests positive after being diluted 64-fold, the titer is 1:64. The higher the titer, the more antibody is present in the blood.

ANCA levels can change over time and may sometimes be used in a general way to monitor disease activity and/or response to therapy; however, titer levels may be inconsistent in some patients, poorly reflecting remission/relapse status.

In addition, tests that are specific for antibodies to MPO and PR3 may be performed:

• A positive test for PR3 antibodies and a positive cANCA or pANCA are seen in more than 80% of patients with active granulomatosis with polyangiitis (Wegener granulomatosis).
• A positive test for MPO antibodies and a positive pANCA are consistent with microscopic polyangitis, glomerulonephritis, eosinophilic granulomatosis with polyangiitis (Churg Strauss syndrome), and Goodpasture syndrome. MPO and pANCA may also be present in other autoimmune disorders, such as systemic lupus erythematosus, rheumatoid arthritis, and Sjögren syndrome.

The following table shows results that may be seen in some vasculitis conditions.

Inflammatory Bowel Disease

ANCA testing can be useful in evaluating patients with symptoms of an inflammatory bowel disease (IBD).

• If atypical ANCA is positive and ASCA (anti-Saccharomyces cerevisiae antibodies) is negative, then it is likely that the person has ulcerative colitis (UC).
• If atypical ANCA is negative and ASCA is positive, then it is likely that the person has Crohn disease (CD). A person who is negative for ANCA and/or ASCA may still have UC, CD, or another IBD.

In most cases, a biopsy of an affected blood vessel is necessary to confirm a diagnosis of autoimmune vasculitis.

Since the symptoms associated with vasculitis and inflammatory bowel disease may be seen with a number of conditions, other tests are frequently performed prior to or along with ANCA testing to rule out other causes for the symptoms.