Antibodies are molecules that are found in the blood stream. They are mainly there to fight infections by targeting foreign molecules. ANCA (anti-neutrophil cytoplasmic antibodies) stick to molecules found in white blood cells rather than to foreign material. These antibodies are often found in the blood of patients with small vessel vasculitis (SVV). It is not clear whether ANCA cause vasculitis, but they can be very helpful in the diagnosis. Unfortunately similar antibodies may be found in other diseases, and not all vasculitis may be ANCA positive, so the test is not 100% reliable as a way of making a diagnosis.
Cerebral angiography and magnetic resonance imaging , family medical history, symptoms, a complete physical examination, and ultimately biopsy of the brain, are often required for the diagnosis. Also, many lab tests must be done for the diagnosis; tests may reveal anemia (a shortage of red blood cells), a high white blood cell count , a high platelet count , allergic reactions, immune complexes, antibodies (tools the body uses to fight off threats) and elevation of inflammatory markers.  Another crucial part in the diagnosis of cerebral vasculitis is the use of imaging techniques. Techniques such as conventional digital subtraction angiography (DSA) and magnetic resonance imaging (MRI) are used to find and monitor cerebral involvement.