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Why We Don’t Use Blood Tests for Food Allergies in Dogs and Cats

Blood tests for food allergies in dogs is a very intriguing proposition; after all, who wants to spend 8 weeks doing a diet trial to get an answer, when you could just have your vet draw some blood and get in answer in a few days? Well, there are reasons that sometimes the easiest answer isn’t always the best one. First of all, food allergies in dogs aren’t as uniform or predictable as food allergies in people. Whereas people can have IgE-mediated, anaphylactic reactions to foods (think peanut allergies in children), this type of reaction is very rare in dogs. While some dogs react to foods immediately (and occasionally severely), some dogs may take up to 7-10 days to react to a protein they ate today. Of the four different hypersensitivity types that are studied in human and veterinary medicine, food allergies in dogs have shown aspects of all four. Moreover, IgE, the immunoglobulin most associated with allergies in human and veterinary literature, is not always a reliable predictor of food allergies in dogs.

What is serum allergy testing?

Many veterinarians (even veterinary dermatologists) will use serum tests to test dogs for environmental allergies. These tests measure allergen-specific IgE in the blood for a host of environmental factors that a pet may be allergic to (dust, pollen, mold, dander, etc.). This is a helpful option for dogs that cannot be sedated for skin testing, or cannot come off of certain medications (such as steroids) long enough for skin testing to be performed. These tests have proven as repeatable, reliable and accurate for this purpose (environmental allergy testing) as our gold standard test, intradermal (skin) allergy testing. Unfortunately, the same cannot be said for food allergy testing.

What is the evidence for serum allergy testing for food allergies?

Whenever a task force of the best and brightest minds in veterinary medicine is assembled, and they review the best available medical evidence, they come to the same conclusions: That the accuracy and repeatability of these tests is low, and that these tests should not be used to diagnose food allergies in dogs or cats. While there is constantly new research being done to try to discover new lab tests (such as patch and prick testing) that may be accurate to diagnose food allergies, so far no method of testing has proven accurate and repeatable enough to be recommended in place of an elimination diet trial.

What kinds of tests are out there?

There are many commercial tests out there that offer to test your dog’s blood, serum, hair, saliva or urine for environmental or food allergies. These tests may range in price from under $100 to hundreds of dollars. The results often come in a folder with several pages of data, explaining testing methods, and usually a results page with numerous food allergies listed, ranging from common proteins (chicken, beef, dairy, etc.) to more obscure ingredients such as butternut squash, cranberries, and flaxseed (I have seen many of these results brought to me by clients in my clinic on an almost weekly basis). While some of these tests are performed by well-established, reputable laboratories (the same labs that we use for the environmental allergy testing listed above), there are some tests run by lesser-known labs (often at a cheaper cost) that border on the fraudulent.  

Regardless of the lab performing the test, or the cost of the test performed, I routinely tell my clients that these tests are a waste of time and money, and that the only accurate and reliable test that currently exists for food allergies in dogs and cats is an elimination diet trial.

  A few general rules about food allergies (that illustrate the weaknesses of these tests):
  1. Food allergies are typically to PROTEINS (with wheat and corn as notable exceptions). I have yet in my career to see a true fruit or vegetable allergy in an animal. If you have run an allergy test that says your dog is allergic to cranberries, it is probably blowing smoke.
  2.  Allergies require exposure over time. If your allergy test says your dog is allergic to something it has never eaten before (such as flax, acai, or amaranth), your test is probably bogus.
  3. If a website or Facebook group is offering you a “faster, easier, cheaper” solution than what your veterinarian is offering you, it is probably too good to be true. If your veterinarian recommends blood allergy testing for food allergies in your dog or cat, please refer them to the website, and the journal articles in the hyperlinks included in this article (especially this one). Even if your friends (or veterinarian) think they are helping you out by recommending these tests, your money could be better spent elsewhere.