Anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) is a group of autoimmune diseases in which small blood vessels are mistakenly attacked and damaged by the immune system.
This attack is caused by self-reactive antibodies, known as ANCAs, that activate white blood cells called neutrophils and trigger an immune response towards the cells lining blood vessels.
The vascular damage in AAV can happen in different organs and tissues, and each patient has their own constellation of symptoms, which can also change over time, depending on the regions affected. The kidneys, skin, and lungs are the most commonly affected organs.
AAV is diagnosed by an assessment of clinical history and a combination of tests, including a physical exam, blood testing, imaging scans, and tissue examination (biopsy) that confirms diagnosis.
Clinical evaluation and physical exam
The diagnosis of AAV can be challenging, owing to its rarity and broad symptoms. When multiple organ systems are involved, many symptoms may arise, and the recognition of an inflammatory disease pattern within these symptoms is key to establish the diagnosis.
As such, a detailed patient history and physical examination to assess all symptoms are crucial to rule out other causes, and to evaluate the severity of the disease and organ involvement.
Blood test
If a patient’s clinical assessments suggest AAV, doctors will request a blood analysis to measure a number of inflammatory, kidney, and immune system proteins.
While measuring ANCA levels in the blood is part of routine clinical care and helps to predict relapses in AAV patients, the test cannot be used alone to diagnose AAV. This is because not all AAV patients test positive for these autoantibodies, and some people without AAV have ANCAs in circulation.
Additional tests include measurements of inflammatory markers, such as C-reactive protein and erythrocyte sedimentation rate, which are higher than normal in cases of inflammation. Creatinine, a metabolic waste product, can also be used to determine kidney function.
Patients may be tested for different autoantibodies that target proteins in the cell’s nucleus or in the glomeruli — the region in the kidneys responsible for filtering out blood — to exclude other conditions with similar clinical signs and symptoms, such as systemic lupus erythematosus.
Among patients with cough or shortness of breath, a full blood count is particularly important to determine hemoglobin levels. Lower levels of this protein, which works to carry oxygen in red blood cells, may indicate bleeding in the airways, bleeding that is undetectable by chest examination.
Urine test
Urine tests are useful to test for the presence of blood and protein in urine, which may indicate a high probability of AAV. These tests are also used to quantify other substances in urine, such as urea (a naturally occurring molecule that is produced by protein metabolism) and electrolytes (minerals that are vital to many key functions in the body).
Biopsy
After clinical features of AAV have been identified and tests suggest the disease, a patient can undergo a tissue biopsy to help confirm the diagnosis.
A biopsy is a procedure wherein a small piece of tissue is removed from an affected tissue or organ to be examined under the microscope. When kidney involvement is suspected, a biopsy can confirm the diagnosis. Lung or skin biopsies may also be taken to confirm a diagnosis of AAV or rule out other conditions such as cancer.
Other tests
Imaging scans, including X-rays and computed tomography, of the chest may be performed to check for lung involvement, and to rule out lung cancer or infection.
Additional tests may include bronchoscopy, a method in which a thin tube with a camera (bronchoscope) goes into the airways and lungs through the nose or mouth.
An endoscopic sinus exam — a procedure where a flexible tube with a light and camera is inserted inside the nose to look at the sinuses — may also be used to detect sinus inflammation, or sinusitis, a very common feature in AAV patients.
Last updated: May 17, 2021
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