ANCA-associated vasculitis (AAV) is a group of autoimmune diseases in which the immune system attacks small blood vessels throughout the body, causing inflammation and damage to organs. The “ANCA” part refers to specific antibodies (antineutrophil cytoplasmic antibodies) that mistakenly target proteins on white blood cells, triggering a chain reaction of inflammation. It’s rare, affecting roughly 12 new people per million adults each year, but it can be serious and requires long-term treatment.
The Three Types of AAV
AAV comes in three distinct forms, each with its own pattern of organ involvement. All three can affect the kidneys, lungs, and other organs, but they tend to do so in different ways.
Granulomatosis with polyangiitis (GPA) primarily targets the upper and lower respiratory tract. People with GPA often develop chronic sinus problems, nosebleeds, and lung nodules. It can also cause rapidly progressive kidney failure. GPA is most strongly linked to a specific type of ANCA that targets a protein called PR3.
Microscopic polyangiitis (MPA) hits the kidneys hardest. Kidney involvement is nearly universal in MPA, typically showing up as sudden kidney failure with blood and protein in the urine. Lung involvement is less common than in GPA, but when it occurs it can cause severe bleeding into the air sacs. MPA can also cause scarring in the lungs (pulmonary fibrosis), sometimes even before other vasculitis symptoms appear. MPA is most associated with ANCA targeting a protein called MPO.
Eosinophilic granulomatosis with polyangiitis (EGPA) stands apart from the other two. It has a strong allergic component, typically developing in people with adult-onset asthma. EGPA can affect the heart, digestive tract, skin, and peripheral nerves. Only 25% to 40% of people with EGPA test positive for ANCA at all, compared to the majority of GPA and MPA patients.
How ANCA Antibodies Cause Damage
In a healthy immune system, white blood cells called neutrophils fight infections. In AAV, the immune system produces antibodies that bind to proteins sitting on the surface of those neutrophils. When ANCA antibodies latch onto a neutrophil, they activate it in the wrong place and at the wrong time, causing the neutrophil to release damaging enzymes directly into the walls of small blood vessels.
This process creates a self-reinforcing cycle. Activated neutrophils trigger the complement system, a part of the immune system that normally helps clear infections. One product of that activation, a molecule called C5a, attracts even more neutrophils to the area and primes them to be activated by more ANCA antibodies. The result is escalating inflammation that damages vessel walls and, by extension, whatever organ those vessels supply.
Common Symptoms
AAV often starts with vague, whole-body symptoms: fatigue, fever, muscle pain, and unexplained weight loss. These can persist for weeks or months before organ-specific problems develop, which makes early diagnosis tricky.
Organ-specific symptoms depend on which type of AAV a person has, but the most commonly affected systems are:
- Kidneys: Blood in the urine, foamy urine from protein leakage, high blood pressure, and in severe cases, rapid loss of kidney function. Kidney involvement is especially common in MPA and GPA.
- Lungs: Persistent cough, shortness of breath, and coughing up blood. GPA tends to cause lung nodules, while MPA is more likely to cause bleeding from tiny capillaries in the lungs.
- Nerves: Numbness, tingling, or weakness in the hands and feet, particularly in EGPA. This happens when inflamed blood vessels cut off the blood supply to peripheral nerves.
- Upper airways: Chronic sinusitis, nosebleeds, ear infections, and hoarseness, most typical in GPA. In rare cases, GPA can narrow the windpipe.
How AAV Is Diagnosed
Diagnosis typically starts with blood tests looking for ANCA antibodies. The two main types are PR3-ANCA (strongly associated with GPA) and MPO-ANCA (more common in MPA and EGPA). A positive ANCA test in someone with the right combination of symptoms raises strong suspicion, but it’s not enough on its own. Some people with AAV test negative for ANCA, and some people with positive tests don’t have vasculitis.
A tissue biopsy, usually from the kidney, lung, or skin, provides the most definitive confirmation. Pathologists look for signs of blood vessel inflammation and, in GPA and EGPA, clusters of immune cells called granulomas. Kidney biopsies in AAV typically show a distinctive pattern of inflammation in the filtering units with very little antibody deposited in the tissue, a finding described as “pauci-immune” glomerulonephritis.
Urine tests also play a key role. Active kidney involvement shows up as red blood cells and protein in the urine, often before a person notices any kidney-related symptoms.
Treatment: Induction and Maintenance
Treatment happens in two phases. The first phase, called induction, aims to shut down active inflammation as quickly as possible. This typically takes about six months. The standard approach combines high-dose steroids with either rituximab (an infusion that depletes certain immune cells) or cyclophosphamide (an older but effective immune suppressant). A landmark trial published in the New England Journal of Medicine established that rituximab is not inferior to cyclophosphamide for achieving remission, and it has become the preferred option for many patients.
Once remission is achieved, the second phase focuses on keeping the disease quiet. Current European guidelines recommend rituximab as the first choice for maintenance, with alternatives available for people who can’t tolerate it. Maintenance therapy generally continues for 24 to 48 months after remission. People who have relapsed before or who carry other risk factors for flares may stay on treatment longer, though this has to be weighed against the risks of prolonged immune suppression, including increased susceptibility to infections.
A Newer Option: Breaking the Inflammation Cycle
Avacopan, approved by both the FDA and European regulators, works differently from traditional treatments. Rather than broadly suppressing the immune system, it blocks the receptor for C5a, the molecule responsible for that self-reinforcing cycle of neutrophil activation described earlier. By interrupting this loop, avacopan reduces vessel damage while allowing patients to use lower doses of steroids. It’s approved for severe GPA and MPA as an add-on to standard therapy, not as a standalone treatment.
Monitoring for Relapse
AAV is a relapsing disease, and ongoing monitoring is a central part of living with it. Regular blood and urine tests help catch flares early, before they cause significant organ damage.
One of the simplest and most effective monitoring tools is a home urine dipstick test for blood. For someone in remission whose urine has been clear, a positive dipstick reading is a signal to contact their care team for a more detailed urine analysis under a microscope. Interestingly, research has found that patients themselves can often sense a flare coming. One study showed that patients could predict disease flares up to three months before their physicians or any clinical test detected them, likely because they notice subtle changes in energy, joint comfort, or general well-being before lab values shift.
ANCA levels are sometimes tracked over time, but a rising ANCA level alone doesn’t reliably predict a flare. Researchers are investigating newer biomarkers, including a urine marker called sCD163, which appears to distinguish active kidney inflammation from remission. For now, though, the combination of regular lab work, urine monitoring, and paying attention to how you feel remains the practical standard.
Long-Term Outlook
AAV is a serious condition, but outcomes have improved substantially over the past few decades with modern immunosuppressive therapy. Survival rates vary depending on the subtype, severity at diagnosis, and how quickly treatment begins. A large multicenter study tracking patients over 15 years found cumulative survival rates of 84% at one year, 76% at three years, and 57% at five years. These numbers reflect a mixed population that includes people diagnosed with severe organ damage, so individual prognosis can differ significantly based on how early the disease is caught and treated.
The kidneys are the organ most at risk for lasting damage. People who start treatment before significant kidney function is lost tend to do better long-term. Treatment side effects, particularly infections from immune suppression, also contribute to long-term risk, which is one reason the newer steroid-sparing approaches like avacopan are generating interest. The prevalence of AAV has been rising in recent years, from roughly 79 per million adults in 2004 to 144 per million in 2016 in one well-tracked population, likely reflecting both better recognition and improved survival keeping more patients in the prevalence pool.