Intradermal Allergy Testing
Also Known As:
IDAT, Intradermal skin testing (IDST), Skin allergy testing
The purpose of an IDAT is to identify the individual allergens your pet is allergic to. Your veterinarian can then recommend avoidance of those allergens when possible and also can determine which allergens should be included in your pet’s allergy vaccine.
A small rectangle is shaved on one side of the patient’s body. Approximately 50 allergens are injected in a sequential pattern. These allergens consist of various grass, weed, and tree pollens, molds, some insects, and household allergens (e.g. house dust mites). If a patient is allergic to an allergen, the specific allergen injection site will become red and swollen (hive) within 15 minutes. Most patients need a small amount of reversible sedation for the procedure in order to avoid discomfort from the injections and ease any anxiety.
The diagnosis of environmental allergies is reached by confirming the presence of appropriate clinical signs and ruling out other causes of itching e.g. food allergies, parasites, skin infections. Therefore, prior to allergy testing for environmental triggers, your veterinarian will want to rule out other potential allergies such as food allergy and flea allergy. Furthermore, your veterinarian will ensure that your pet is clear of infection at the site of the test in order to prevent any false positive reactions. Medications such as steroids, antihistamines, and fatty acids will need to be discontinued prior to allergy testing as these medications can suppress allergic reactions and result in a false negative test. The “wash out” periods are as follows:
Long-acting injectable steroids: 6-8 weeks
Oral steroids (i.e. prednisone, dexamethasone, Temaril-P, etc.): 4 weeks
Topical steroids (i.e. Gen-One spray, Gentizol, Mometamax, hydrocortisone, etc.): 2 weeks
Antihistamines (i.e. Benadryl, Zyrtec, etc.): 2 weeks
Fatty acids (i.e. fish oil, flaxseed oil, etc.): 2 weeks
Your veterinarian will formulate an allergy vaccine specifically for your pet based on the results of the allergy test. The vaccine can be made into an injectable form or as drops that are given in the mouth. Injections are usually given weekly and drops are usually given twice a day. It is important to understand that while this is the best long term therapy for your allergic pet, it can take 3-12 months to see a full response. While awaiting response to the immunotherapy, your pet may need to remain on medications to keep their allergy symptoms at bay.
Why Skin Testing vs. Blood Testing?
Unfortunately blood allergy tests have some inherent problems in their design. They were initially developed for humans and the circulating antibodies that they test for are different in dogs and cats than in people. The result is that there are a lot of false positives. In other words, the test results indicate that your animal is allergic to things that he is really not. For this reason, veterinary dermatologists opt for intradermal skin testing. However, periodically blood testing is used in special circumstances in which intradermal skin testing cannot be performed, such as:
- The skin is too unhealthy to test either due to infection or severe inflammation.
- Prolonged drug withdrawal for antihistamines and corticosteroids cannot be tolerated.
- The dog is very young.
- The dog is a show dog whose hair cannot be clipped.
- The intradermal skin test (IDST) is negative, yet atopy is still suspected.