The Bottom Line: In 1990, the American College of Rheumatology (ACR) defined the classification criteria to distinguish between the different vasculitides and identified six criteria for EGPA, namely asthma, eosinophilia >10%, neuropathy, non-fixed lung infiltrates, paranasal sinus abnormalities and extravascular eosinophils on biopsy. When four or more of these criteria are met, vasculitis can be classified as EGPA with a sensitivity of 85% and a specificity of 99.7% (Greco et al, 2015).
References: Bui VL, Kermani TA. Clinical significance of a positive antineutrophil cytoplasmic antibody (ANCA) test. JAMA. 2016 Sept 6; 316(9):984-985. doi:10.1001/jama.2016.8307.
Greco A, Rizzo MI, Di Virgilio A, et al. Churg-Strauss syndrome. Autoimmunity Reviews. 2015 Apr; 15(4):341-348. doi: 10.1016/j.autrev.2014.12.004.