The ANCA – Serine Proteinase 3 (c-ANCA) test is a blood test that measures the levels of a type of antibody called antineutrophil cytoplasmic antibodies (ANCA) in the blood. c-ANCA specifically targets the serine proteinase 3 (PR3) antigen, which is found in certain white blood cells called neutrophils. The c-ANCA test is commonly used to diagnose and monitor autoimmune diseases that affect the blood vessels, such as granulomatosis with polyangiitis (GPA), previously known as Wegener’s granulomatosis. Elevated levels of c-ANCA in the blood can indicate inflammation of the blood vessels and tissue damage, while low levels may be a sign of remission or response to treatment. The c-ANCA test involves taking a small sample of blood, which is then analyzed in a laboratory to determine the levels of the antibody. Depending on the results of the test, doctors may recommend additional diagnostic tests or treatments to address underlying conditions. Regular monitoring of c-ANCA levels can also be used to track the progression of autoimmune diseases and evaluate the effectiveness of treatment.