This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology and Rheumatology, Subject name: Medicine
[{'content': 'A patient presenting with cutaneous vasculitis, glomerulonephritis, and peripheral neuropathy. Which investigation is to be performed next that will help you diagnose the condition? \nSelect and explain. \nA. ANCA, B. RA factor, C. HbsAg, D. MIF', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (A) ANCA [?]ANTINEUTROPHIL CYTOPLASMIC ANTIBODIES (ANCA):oANCA are antibodies directed against certain proteins in the cytoplasmic granules of neutrophils & monocytes.oAs in the given question case history:-ANCA are present in a High percentage of patients with active granulomatosis with Polyangiitis (Wegener\'s) & Microscopic Polyangiitis.-ANCA present with a Lower percentage of patients with Eosinophilic Granulomatosis with Polyangiitis (Churg- Strauss).oThese diseases share the presence of ANCA & small-vessel vasculitis, some investigators have come to refer to them collectively as "ANCA-associated vasculitis."APPLICATIONS OF ANCAPrevalence of ANCA in renal vasculitisType of renal vasculitisANCA test positivity (%) P-ANCAC-ANCA*. Polyarteritis nodosa10-20%10-20%*. Microscopic polyangitis50-80%10-20%*. Wegener\'s granulomatosis10-20%80-90%*. Necrotizing & crescentic GN50-80%10-20% pANCA disease associationcANCA disease: associationAtypical*. Primary vasculitis. Microscopic polyangiitis. Churg-Strauss syndrome. Polyarteritis nodosa*. Collagenosis. Felty\'s syndrome. SLE. Rheumatoid arthritis. Sjogren\'s syndrome*. Chronic inflammatory bowel disease*. Chronic liver disease. Primary sclerosing cholangitis*. Primary vasculitis. Wegener\'s granulomatosis. Microscopic polyangiitis. Churg-Strauss syndrome*. Primary sclerosing cholangitis*. Primary biliary cirrhosis*. Autoimmune hepatitis*. SLE*. RA ANCA ANTI-NEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIS (AAV)Defining featuresClinical RelevanceCHCC 2012 definitions of AAVEvidence that ANCAs are pathogenicGPA:*. Granulomatous inflammation usually involving the respiratory tract*. Small-vessel necrotizing vasculitis*. Necrotizing glomerulonephritis is commonMPA:*. Small-vessel necrotizing vasculitis*. Necrotizing glomerulonephritis is very common*. Pulmonary capillaries often occursEGPA:*. Eosinophil-rich granulomatous inflammation of the respiratory tract*. Small-vessel necrotizing vasculitis*. Blood eosinophlia*. AsthmaClinical evidence:*. Strong association with ANCA (MPA >90%, GPA >90%, EGPA >40%**. Partial correlation of ANCA titre with disease activity*. Correlation of ANCA epitope specificity with disease activity (MPO-ANCA only)*. Disease indication by trans-placental transfer of ANCA (one MPO-ANCA case report)*. Similar disease associated drug-induced ANCA*. HLA genetic associations with MPO-ANCA and PR3-ANCA-assocated disease*. Response to immunosuppressive therapy that targets B cellsIn vitro evidence:*. Activation of cytokine-primed neutrophils by ANCA IgG*. Endothelial injury by ANCA-activated neutrophils*. Alternative complement pathway activation by ANCA-activated neutrophilsEvidence from animal models:*. Induction of pauci-immune vasculitis, glomerulonephritis and graunolomatosis in mice and rats by anti-MPO IgG*. Prevention of murine anti-MPO IgG induced disease by blockade of alternative complement pathway activation or blockade of C8a receptor', 'role': 'assistant'}]