The serum protein profiles were significantly different between active and inactive EGPA, however, Axl, OPN, HCC-4, GDNF and MCP-3 were consistently higher in active disease, with Axl having the largest AUC, indicating that it could be a candidate for a new biomarker of active EGPA. The gene discussed is SPP1; the disease is eosinophilic granulomatosis with polyangiitis.