Why ANCA,IFA test is done An ANCA test is most often used to find out if you have a type of autoimmune vasculitis. There are different types of this disorder. They all cause inflammation and swelling of blood vessels, but each type affects different blood vessels and parts of the body. IFA is an assay which uses fluorescent microscopy to detect antibodies to specific antigenic material. This test is often used to confirm positive results obtained by ELISA (Enzyme Linked Immunosorbent Assay) or MFIA (Multiplexed Fluorometric ImmunoAssay ).