Antineutrophil Cytoplasmic Antibodies (ANCA) Test

The ANCA test is a blood test used to detect the presence of antineutrophil cytoplasmic antibodies in the blood. These antibodies are a type of protein that can be found in the blood of people with certain autoimmune disorders, such as vasculitis.

What are ANCA?

ANCA are antibodies that target and bind to the cytoplasmic components of neutrophils, which are a type of white blood cell. They are normally produced by the immune system to fight off infections, but in people with autoimmune disorders, they can mistakenly attack healthy tissues.

What is the purpose of the ANCA test?

The ANCA test is used to diagnose and monitor autoimmune disorders such as:

• Granulomatosis with polyangiitis (GPA), formerly known as Wegener's granulomatosis
• Microscopic polyangiitis (MPA)
• Eosinophilic granulomatosis with polyangiitis (EGPA), formerly known as Churg-Strauss syndrome

How is the ANCA test performed?

The ANCA test involves taking a blood sample from a vein in the arm. The blood sample is then sent to a laboratory for analysis.

Types of ANCA tests

There are two main types of ANCA tests:

• Indirect immunofluorescence (IIF) test: This test uses a fluorescent dye to detect the presence of ANCA in the blood.
• Enzyme-linked immunosorbent assay (ELISA) test: This test uses an enzyme to detect the presence of ANCA in the blood.

Interpretation of results

The results of the ANCA test can be:

• Positive: The presence of ANCA in the blood, which may indicate an autoimmune disorder.
• Negative: The absence of ANCA in the blood, which may indicate that an autoimmune disorder is unlikely.
• Borderline or equivocal: The results are not clear-cut and may require further testing or evaluation.

Clinical significance

A positive ANCA test result can be associated with:

• Vasculitis, which is inflammation of the blood vessels
• Glomerulonephritis, which is inflammation of the kidneys
• Respiratory symptoms, such as coughing and shortness of breath
• Skin lesions or rashes

A negative ANCA test result does not rule out an autoimmune disorder, as some people with these conditions may not have detectable levels of ANCA in their blood.