Standardization of Beef, Pork, Chicken, and Soy Protein Extracts for Patch Testing and Their Accuracy in Diagnosing Adverse Food Reactions in Dogs with Chronic Pruritus

(1): Background: This study aimed to evaluate the concentrations of four proteins for allergic patch testing (APT) in dogs, assessing sensitivity (SE), specificity (SP), negative predictive value (NPV), positive predictive value (PPV), reactions to adhesives/containers, and the safety of APT with food proteins in dogs. (2) Methods: For evaluation, 43 dogs were screened and divided into two groups: Group 1 consisted of 20 healthy dogs, and Group 2 included 23 dogs with canine atopic dermatitis (AD). Group 1 underwent allergic patch testing (APT) with beef, pork, chicken, and soy proteins at four different concentrations (100 mg, 250 mg, 500 mg, 1000 mg/0.2 mL). Of the 23 dogs included in Group 2, four did not undergo the elimination diet and were excluded, leaving 17 dogs in the study. They underwent an elimination diet (ED) and were evaluated using the pruritus visual analog scale (pVAS) and lesion scores (CADESI-4) before and after the ED (days 0 and 45). After the ED, Group 2 was subjected to APT (using the same proteins and concentrations as Group 1) and an oral provocation test (OPT) with the proteins used in the APT. The results of the OPT were used to assess the accuracy of the APT. (3) Results: In Group 1, one dog reacted to the APT. In Group 2, after 45 days of ED, of the 17 dogs included, 13 showed a reduction in pVAS and CADESI-4 scores (<i>p</i> < 0.05) and nine an improvement considered good to excellent. Of these, two showed irritant contact reactions to the APT chambers and were excluded, leaving 11 dogs that were reactive to APT, and the OPT increased pruritus (<i>p</i> < 0.05). Accuracy: Beef and chicken proteins at concentrations of 500 and 1000 mg/0.2 mL, and soy protein at 1000 mg/0.2 mL, achieved 100% SE, SP, PPV, and NPV. Pork protein at 1000 mg/0.2 mL achieved 100% SE, 83% SP, 83% PPV, and 100% NPV. (4) Conclusions: APT with beef and chicken proteins at 500 mg and 1000 mg/0.2 mL and soy protein at 1000 mg/0.2 mL, based on the results of this study, can be recommended for diagnosing adverse food reactions in dogs with AD.