ANCA Test: (Anti-Neutrophil Cytoplasmic Antibody test)

This test is highly specific for certain autoimmune diseases affecting blood vessels (Churg-Strauss Syndrome, Microscopic Polyangiitis and Wegener's Granulomatosis). It is done by separating out neutrophils (one type of white blood cell) and staining them with a dye that will fluoresce when exposed to ultra-violet light. The illuminated neutrophils are then examined by microscope to determine the character of the fluorescing granules in the neutrophils.

One of four findings may result from the ANCA tests:
1. A test result where the fluorescent granules are scattered in the cytoplasm of neutrophils (positive cytoplasmic or C-ANCA)
2. A test result where the fluorescent granules are mostly near the nucleus of neutrophils (positive perinuclear or P-ANCA).
3. A test result where the fluorescent granules are diffuse, both in the cytoplasm and near the nucleus (positive mixed ANCA).
4. A negative ANCA where so little fluorescence is present, it falls below the upper limit of normal.

Points to consider about ANCA:
1. The upper limit of normal C-ANCA ratio varies from lab to lab. The upper normal limit for the test result to be considered a negative may be about 1:16 or 1:32.
2. The C-ANCA test is about 90+% accurate for WG for serious cases, but only 50% or so for light cases).
3. Not all medical labs do the test, so frequently it is a 'send-out' test. A tentative diagnosis made by positive C-ANCA is often confirmed by biopsy.
4. The related P-ANCA test if positive may be an indicator for some other autoimmune diseases, e.g., microscopic polyarteritis (MPA), Churg-Strauss Syndrome (CSS), or crescentic glomerulonephritis.
5. In the case of mixed ANCA, it may require other tests and analysis of symptoms to determine if the cause of the abnormality is vasculitis or some other condition.
6. The C-ANCA and P-ANCA are immunofluorescent (IIF) tests requiring a human microscopic examination and interpretation. Results may vary if different individuals are doing the test. It is best to have these and other tests done at the same lab each time to reduce the possible variations.
7. While a positive C-ANCA is highly diagnostic for Wegener's, some small percentage of Wegener's patients test P-ANCA positive, rather than C-ANCA. Occasionally a Wegener's patient will switch at times from testing positive to one ANCA to the other.
8. ANCAs are titrated tests. Stained blood samples are diluted in steps, progressively until no fluorescence is detected. Results are reported as the dilution level at which fluorescence ceases. These are given as 1:256 or 1/256 for example. The higher the ANCA ratio, the more of the harmful antibodies are present in the patient's blood.
9. ANCA test results can be positive due to conditions other than autoimmune diseases. Amebiasis, ulcerative colitis, mesangiocapillary glomerulonephritis with crescents, improperly cleaned glassware, and both subacute and bacterial endocarditis have been shown to cause transient positive ANCAs.
10. ANCA test samples can show differing results if submitted to different labs. An effort to standardize these tests is underway in Europe by the EUVAS group. False positives or negatives can and do occur due to mishandling or misinterpretation or even effects of medications or other disease conditions.
11. In diagnosis both C-ANCA by immunofluorescence and anti-PR-3 by ELISA result in greater sensitivity than either test alone, and are often both are performed even if only the C-ANCA is ordered.

Blood Tests

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C Reaction Protein (CRP)