A casein allergy occurs when your body mistakenly identifies casein as a threat to your body. Your body then triggers a reaction in an attempt to fight it off. This is different than lactose intolerance, which occurs when your body doesn t make enough of the enzyme lactase.The Casein Allergy Test is qualitative allergen specific IgE blood test to determine if you are suffering from a hypersensitivity to Casein, the main protein in milk.