Concurrently submitted tests for Anti–membrane attack complex (MAC) antibodies, antinuclear antibodies, myeloperoxidase-anti-neutrophil cytoplasmic antibodies (MPO-ANCA), and proteinase-3-anti-neutrophil cytoplasmic antibodies (PR3-ANCA) were performed to eliminate autoimmune vasculitis; these tests yielded negative results, thereby increasing the likelihood of vasculitis due to pegfilgrastim. This evidence concerns the gene MPO and autoimmune vasculitis.