• Allergic diseases are being recognized with increasing frequency in the cat.
• The development of reliable serological tests to aid their diagnosis has been hampered by the lack of commercially available reagents for anti-feline IgE.
• In 2003, the isolation of feline IgE was achieved and an ELISA test for allergen specific IgE launched Allergy testing. 
• With food allergy, dermatological signs are indistinguishable from those of atopic dermatitis Skin: atopic dermatitis. In 33% of cases, lesions are restricted to the head and neck.
• Gastrointestinal signs (chronic and intermittent diarrhea, and/or vomiting) may occur alone or in conjunction with dermatological signs.
• Blood tests for food allergies are not recommended. Results may not accurately predict the allergens causing clinical signs. 

Uses

Alone

• As a possible aid in selection of food for dietary elimination trial in suspected dietary hypersensitivity Food hypersensitivity.

In combination

• With other diagnostic tests in the investigation of feline atopic dermatitis Skin: atopic dermatitis.
• Most commonly pruritic cats show one or a combination of:
  • Self-induced hair loss.
  • Miliary dermatitis Dermatitis: miliary.
  • Eosinophic plaques Eosinophilic plaque, ulcers or linear granulomas Eosinophilic granuloma complex.
• With other tests for diagnosis of vomiting and diarrhea.

Other points

• Established approach to diagnosis of food allergies causing dermatological signs is elimination diet of 3-10 weeks followed by provocative diet challenge if signs resolve Elimination diets for adverse food reactions.
• Allergen testing and dietary responses to foods do not show consistent results, and it does not test for food intolerances.
• Food allergies commonly co-exist with other hypersensitivities such as atopy Skin: atopic dermatitis and flea hypersensitivity Flea bite hypersensitivity. 
• Ideally, a diet containing a protein not previously fed or a hydrolyzed protein diet should be included in the elimination trial.
• Dermatological signs may take weeks to respond, whereas the majority of cats with gastrointestinal signs due to adverse reaction to food may respond within a week.
• To confirm an adverse reaction to a food, the cat should be challenged with the potentially offending food after signs have resolved; however, many owners are reluctant to do this.
• While dietary elimination trials cannot distinguish between food allergy (immune-mediated) and food intolerance (non-immune-mediated), this may not be clinically relevant to an individual animal.