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.

Frequently Asked Questions (FAQs)

What is the ANCA test used for?
The ANCA test is used to diagnose and monitor autoimmune disorders, such as granulomatosis with polyangiitis and microscopic polyangiitis.

What do ANCA test results indicate?
Positive results may indicate the presence of certain autoimmune diseases, while negative results do not necessarily rule out these conditions.

How is the ANCA test performed?
The test involves a blood sample, which is then analyzed for the presence of ANCA antibodies using various techniques, including indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA).

What are the types of ANCA antibodies?
There are two main types: cytoplasmic ANCA (c-ANCA) and perinuclear ANCA (p-ANCA), which target different proteins.

What is the significance of c-ANCA and p-ANCA?
c-ANCA is often associated with granulomatosis with polyangiitis, while p-ANCA is linked to microscopic polyangiitis and other conditions, such as eosinophilic granulomatosis with polyangiitis.

Can the ANCA test be used to monitor disease activity?
Yes, the test can help monitor disease activity and response to treatment in some cases, but its utility may vary depending on the specific condition.

Are there any factors that can affect ANCA test results?
Certain medications, infections, and other medical conditions may influence test results, potentially leading to false positives or negatives.

What is the sensitivity and specificity of the ANCA test?
The sensitivity and specificity of the test vary depending on the technique used, the population being tested, and the specific condition being diagnosed.

Can a negative ANCA test result rule out autoimmune disorders?
No, a negative result does not necessarily exclude the presence of an autoimmune disorder, as some conditions may be ANCA-negative or have low titers.

Are there any alternative tests to the ANCA test?
Other diagnostic tests, such as biopsy and imaging studies, may be used in conjunction with or instead of the ANCA test to diagnose and monitor autoimmune disorders.