A patient presenting with cutaneous vasculitis, glomerulonephritis, and peripheral neuropathy. Which investigation is to be performed next that will help you diagnose the condition?

(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