Flea allergy dermatitis (FAD) is common in cats. In this study, feline FAD was experimentally induced in 14 cats to determine whether feline basophilic granulocytes could be used as an in vitro diagnostic test for feline FAD. The test, a functional in vitro test (FIT), evaluated spontaneous release of mediators, physical release of mediators, general stimulation of basophils, and sensitization of basophilic granulocytes with antibodies against specific flea antigens. Clinical signs, intradermal reactions to flea antigen, and flea-specific serum IgE levels were monitored in the cats. During the study, only 1 cat developed clear signs of FAD, and 9 cats developed temporary clinical signs consistent with FAD. The study found good agreement between intradermal skin tests and the FIT but poor agreement between the FIT and flea-specific serum IgE levels. Study funded by BayerHealth Care AG

COMMENTARY: This study highlights one of the most important points involving any diagnostic test for "allergy." Positive test results reflect only exposure to fleas-definitive diagnosis of FAD in cats requires a compatible history, clinical signs, and response to flea control. Ideally, it is helpful (for clients) to find evidence of flea infestation, but given the meticulous grooming habits of cats that is not always possible. In my experience, "flea allergy testing" in cats and finding a "positive" test are most useful for convincing clients to do a trial of flea control. Currently, FIT is experimental and not widely available. The cost of serum in vitro testing for flea antigen may be equivalent to a flea control trial. Intradermal testing (IDT) is an option in private practice, but there is a start-up cost to the practice to purchase the controls and antigen and needles, and it can be a major hassle to do even a small IDT on a cat, depending on its mood that day. FIT may be an option in the future; at one time serum in vitro testing was an experimental tool only.

Monitoring of basophil sensitization to antigens of the cat flea (Ctenocephalides felis felis): A new tool for the diagnosis of feline flea bite hypersensitivity? Stuke K, von Samson-Himmelstjerna G, Dressman. J PARASITOL RES 103:807-820, 2008.