Measurement of IgE to galactose alpha-1,3-galactose (α-Gal sIgE) is used in the differential diagnosis of α-Gal mediated allergy. There are two distinct forms of this allergy: the first is an immediate-onset anaphylaxis observed following intravenous infusion of Cetuximab, a monoclonal antibody against epidermal growth factor receptor, and the second is a delayed-onset allergy or anaphylaxis that occurs several hours following consumption of red meat. Bites from certain ticks, such as the Lone Star Tick in the United States, have been implicated in the development α-Gal allergy. Furthermore, α-Gal may be helpful in elucidating the allergen responsible in patients initially diagnosed as having ‘idiopathic’ anaphylaxis or urticaria.