A 5-year-old girlcame to the Emergency Dept. in evening with the complaint of sudden onset of "difficulty in breathing" and fever,pruritus.She has no past history of lung infection, no recent travel history. She have an history of pica. Little kid is worried about his puppy at home during his hospital stay. On Examination wheezing and hepatomegaly is present. On Peripheral smear, marked eosinophilia,leucocytosis is seen. Best test that helps in diagnosis?