ANCA test explained: antineutrophil cytoplasmic antibodies

ANCA are autoantibodies that the immune system mistakenly produces against proteins in the cytoplasm of neutrophils (a type of white blood cell). Instead of defending the body against infections, these antibodies can cause inflammation of the blood vessel walls — vasculitis. According to MedlinePlus, the test establishes whether ANCA are present in the blood and, if they are, what type they are (most often the c-ANCA and p-ANCA subtypes are distinguished), because that helps to tell apart the specific variant of vasculitis. A positive ANCA is linked with diseases such as granulomatosis with polyangiitis (which damages the lungs, sinuses, nose, trachea and kidneys) and microscopic polyangiitis (which damages the lungs, kidneys, nerves, skin and joints). It is also characteristic of eosinophilic granulomatosis with polyangiitis (which damages the lungs, sinuses, stomach, intestines, skin, heart and nervous system). A positive ANCA is sometimes also found in ulcerative colitis. Because the result is qualitative (positive/negative) rather than a numeric reference range, it always has to be assessed together with symptoms and other tests.

• When there are signs of vasculitis — tiredness, fever, joint and muscle pain, loss of appetite or weight loss
• When changes in vision, ringing in the ears or hearing loss appear
• When a rash, bruising, bleeding when coughing or shortness of breath is noticed
• When blood appears in the urine, or there is numbness or tingling
• When there is abdominal pain, diarrhoea or bloody stools — when inflammatory bowel disease is suspected
• To monitor the course of treatment of an already diagnosed vasculitis

A positive ANCA means that antineutrophil cytoplasmic antibodies have been found in the blood, and according to MedlinePlus this may point to vasculitis — inflammation of the blood vessels. Once the antibody type is established, it becomes possible to narrow down which variant of vasculitis is most likely, but the final diagnosis is confirmed by a doctor together with other tests and symptoms.

What can lie behind a positive result

• Granulomatosis with polyangiitis (GPA) — damages the lungs, sinuses, nose, trachea and kidneys
• Microscopic polyangiitis (MPA) — damages the lungs, kidneys, nerves, skin and joints
• Eosinophilic granulomatosis with polyangiitis (EGPA) — damages the lungs, sinuses, stomach, intestines, skin, heart and nervous system
• Ulcerative colitis
• A family history of autoimmune diseases, chronic infections or exposure to environmental toxins — factors that make it easier for the immune system to produce these autoantibodies

Symptoms that can accompany a positive result

• Tiredness, fever, muscle and joint pain
• Loss of appetite and weight loss
• Changes in vision, ringing in the ears, hearing loss
• Rash, bruising
• Coughing up blood, shortness of breath
• Blood in the urine, numbness, tingling
• Abdominal pain, diarrhoea, bloody stools

What to discuss with a doctor

• Which type of antibodies was found (c-ANCA or p-ANCA) — this helps to narrow down the possible variant of vasculitis
• Further tests and assessment of organ function (for example the kidneys or the lungs), depending on the symptoms
• Discussing the symptoms with a doctor, since a positive ANCA on its own does not confirm a diagnosis
• If vasculitis has already been diagnosed — repeating the test to monitor the course of treatment

Other autoantibody tests explained here

• ANA — antinuclear antibodies
• Rheumatoid factor
• Anti-CCP
• Anti-dsDNA
• Anticardiolipin antibodies