Disclosed is a method for diagnosing allergy in a human or animal patient, wherein the level of species-specific lipocalin, especially lipocalin 2 in a human patient, is measured in a sample of said patient and wherein a lowered level of said lipocalin compared to the level of said lipocalin in the corresponding sample of a human or animal that has no allergy, is indicative of an allergy, as well as a kit for performing this method, and a kit for quality control of allergen molecules or extracts used for immunotherapy of allergy by determining its siderophore-iron ligand load and thus immunomodulatory potency. Further, lipocalin proteins for use in treatment or prevention of allergies are provided, preferably complexed with siderophore-iron ligands.