Test Details: The substance causing allergy, when inhaled or eaten is called an allergen. An allergen activates the immune system by producing specific antibodies against it. One such kind of allergy is the allergy to milk or milk products sach as curd (dahi) containing protein casein. This test helps to detect the presence and level of specific antibody Immunoglobulin E (IgE) in the blood sample against this allergen.