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The ANCA (Anti-Neutrophil Cytoplasmic Antibodies) test is a medical blood test used to diagnose and monitor various autoimmune disorders. ANCA is a type of autoantibody that targets the neutrophil cytoplasm of healthy white blood cells. The test detects the presence of these antibodies in the blood, which can be a hallmark of certain conditions.

There are several types of ANCA tests, each detecting different antibodies. The most common types are perinuclear ANCA (p-ANCA) and cytoplasmic ANCA (c-ANCA). p-ANCA is typically associated with conditions such as microscopic polyangiitis, primary sclerosing cholangitis, and inflammatory bowel disease. c-ANCA, on the other hand, is often found in patients with granulomatosis with polyangiitis (formerly known as Wegener's granulomatosis) and eosinophilic granulomatosis with polyangiitis.

The ANCA test is not used as a standalone diagnostic tool, but rather as a complementary test to help confirm a diagnosis or rule out other conditions. A positive ANCA test may indicate an underlying autoimmune disorder, but it does not necessarily confirm a diagnosis. The results should be interpreted in conjunction with clinical findings and other laboratory tests.

ANCA tests are typically performed on patients with symptoms suggestive of an autoimmune disorder. These symptoms may include fever, joint pain, kidney problems, and blood vessel inflammation. The test is usually conducted using an enzyme-linked immunosorbent assay (ELISA) or immunofluorescence technique. The results are reported as either positive or negative, and in some cases, the level of ANCA antibodies in the blood may be quantified.