A pilot study of the validation of percutaneous testing in cats Michael A. Rossi*,†, Linda Messinger*, Thierry Olivry† and Raweewan Hoontrakoon‡ *Veterinary Referral Center of Colorado (Dermatology/Allergy), 3550 South Jason Street, Englewood, CO 80110, USA †Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA ‡Premier Allergy and Asthma, 18525 East Smoky Hill Road Suite C, Aurora, CO 80015, USA Correspondence: Michael A. Rossi, Veterinary Referral Center of Colorado (Dermatology/Allergy), 3550 South Jason Street, Englewood, CO 80110, USA. E-mail: mrossi@vrcc.com Background – Intradermal testing is useful for the identification of environmental allergens to which cats could be hypersensitive; intradermal test reactions are often subtle and difficult to interpret in cats. Percutaneous test- ing is the standard technique for the detection of significant environmental allergens in people, but it has not yet been evaluated in cats with hypersensitivity dermatitis. Hypothesis/Objectives – The purpose of this study was to evaluate and compare the skin test responses of healthy cats to percutaneous application and intradermal injections of control solutions. Methods – Ten clinically healthy cats were studied. Percutaneous applications of 0.0275 and 0.1 mg/mL aque- ous histamine, 6 mg/mL glycerinated histamine, 0.9% buffered saline and 50% glycerosaline solution were per- formed using Greer Pick (Greer Laboratories, Lenoir, NC, USA) and Duotip-Test II (Lincoln Diagnostics, Decatur, IL, USA) percutaneous applicators. Reactions were compared with intradermal injections of 0.0275 mg/mL aque- ous histamine and 0.9% buffered saline as controls. Results – Positive responses to histamine solutions were significantly greater with the Greer Pick than with the Duotip-Test II. There were no significant differences between the histamine reactions using the Greer Pick appli- cator and the intradermal injections. Percutaneous reactions to histamine were more well demarcated and easier to read than intradermal injection reactions. Reactions to the saline controls were not noted. Conclusions and clinical importance – Percutaneous application of 6 mg/mL glycerinated histamine solution, 50% glycerosaline solution and 0.9% buffered saline produced similar positive and negative control wheals. These observations warrant further studies of percutaneous allergen testing in cats with hypersensitivity dermatitis. Introduction Feline hypersensitivity dermatitis is a common skin dis- ease of cats with a wide range of clinical presentations, including but not limited to the following: miliary dermati- tis; feline eosinophilic diseases (the so-called ‘eosinophilic granuloma complex’, i.e. indolent ulcers, eosinophilic granulomas and plaques); self-induced, usually symmetri- cal alopecia; head/neck pruritus; and allergic asthma. 1–3 The diagnosis and treatment of environmental aller- gies in cats is based upon suggestive history, clinical signs and exclusion of other pruritic dermatoses, as well as demonstration of allergen-specific hypersensitivity. This last parameter is assessed via allergen-specific IgE serology and/or intradermal testing (IDT). Intradermal testing is a useful tool for allergen identification in the dog and horse; however, skin reactions to allergens injected intradermally are often weak in cats, and wheals may be difficult to evaluate, even those of the histamine positive control. 4 Novel methods to increase the sensi- tivity of IDT in cats have been attempted, including the use of intravenous fluorescein dye to better visualize positive reactions to injected allergens. 5 This procedure, while useful, is limited due to the availability of fluores- cein, as well as the potential for rare, mild to severe adverse events related to the intravenous injection of the dye, which have included nausea, vomiting and ana- phylaxis. 6,7 Percutaneous testing (PT) has been the standard tech- nique used by allergists since it was described by Lewis and Grant in 1926 for the confirmation of allergic reac- tions in humans. 8 Percutaneous testing, also known as ‘prick test’, is performed by using a special applicator con- taining a concentrated amount of various allergens to scratch/prick the surface of the skin. If an IgE-mediated hypersensitivity is present, a wheal and flare response will manifest, which is then measured both objectively and subjectively. If the reaction is deemed to be positive, then that allergen is considered for inclusion in the aller- gen-specific immunotherapy (ASIT) formulation. This method of PT has been attempted in dogs with atopic dermatitis; however, the results were found not to be as Accepted 22 May 2013 Sources of Funding: Testing materials were supplied by and the study was partly funded by Greer Laboratories, Lenoir, NC, USA. Conflicts of Interest: No conflicts of interest have been declared. This study was published as an abstract of the North American Veterinary Dermatology Forum 2013, Louisville, KY, USA, in Vet- erinary Dermatology 2013; 24: 305. © 2013 ESVD and ACVD, Veterinary Dermatology , 24, 488–e115. 488 Vet Dermatol 2013; 24: 488–e115 DOI: 10.1111/vde.12054