ANCA (antineutrophil cytoplasmic antibodies)
An autoantibody test that helps diagnose a group of small-vessel inflammatory diseases called ANCA-associated vasculitis. A positive result, especially with inflammation and kidney signs, points toward these conditions — but it is always read alongside the clinical picture.
What it measures
ANCA are antibodies the immune system makes, wrongly, against proteins inside a type of white blood cell called a neutrophil. Their main use is in diagnosing and monitoring ANCA-associated vasculitis — a group of autoimmune diseases in which small blood vessels become inflamed, including granulomatosis with polyangiitis, microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis. The test is usually reported in two ways that give complementary information: a staining pattern seen under the microscope (cytoplasmic, c-ANCA, or perinuclear, p-ANCA) and the specific target antigen (PR3 for c-ANCA, MPO for p-ANCA). A positive ANCA in someone with the right clinical picture — such as unexplained inflammation, kidney involvement, lung symptoms, sinus disease or a rash — strongly supports the diagnosis and helps guide urgent treatment. However, ANCA can occasionally be positive in other conditions or negative in genuine vasculitis, so it is never used alone. It is checked together with markers of inflammation (CRP, ESR) and kidney function (creatinine, urea), because these diseases can damage the kidneys quickly.
What a high value can mean
- ANCA-associated vasculitis — the main reason the test is done; a positive result supports diseases such as granulomatosis with polyangiitis or microscopic polyangiitis.
- c-ANCA / anti-PR3 — most associated with granulomatosis with polyangiitis.
- p-ANCA / anti-MPO — most associated with microscopic polyangiitis and some other conditions.
- Occasionally positive in other autoimmune or inflammatory bowel conditions — which is why it is read with the clinical picture.
High ANCA (antineutrophil cytoplasmic antibodies): full guide
What a low value can mean
- Negative — the expected, normal result; makes ANCA-associated vasculitis less likely.
- A falling titre during treatment — can suggest the disease is responding, though it is not a perfect guide.
Low ANCA (antineutrophil cytoplasmic antibodies): full guide
When to discuss with a doctor
ANCA is a specialist test, requested when a doctor suspects small-vessel vasculitis — for example because of unexplained inflammation, kidney abnormalities, blood in the urine, lung or sinus symptoms, nerve problems or a purpuric rash. A positive result in that setting supports the diagnosis and often prompts urgent specialist assessment, because these conditions can damage the kidneys and other organs quickly and are very treatable when caught early. Because ANCA can be falsely positive or negative, it is always interpreted with the symptoms, the inflammation and kidney markers, and often a biopsy. Mediora.AI shows ANCA alongside CRP, ESR and kidney function so the vasculitis pattern is visible; the diagnosis and treatment belong with your doctor and specialist team.