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Nutrition Nuggets is the newest offshoot of petMD's Dog Nutrition Center. Each week Dr. Coates will use her expertise and wisdom to blog about the intricacies of dog nutrition.

Help in Diagnosing Food Allergies?

December 14, 2012 / (11) comments

Diagnosing canine food allergies is no fun at all. The condition’s most common symptoms of itching and chronic/recurrent skin and ear problems (with or without concurrent GI signs) are hardly unique to food allergies, so a complete work-up is the first order of business. And then finally, when we get to the point where we’re highly suspicious that a food allergy is to blame for a dog’s misery, we have to institute a food trial that lasts from eight to twelve weeks, during which time a dog eats absolutely nothing except an elimination diet and water (no treats, no flavored heartworm preventives … nothing).


An elimination diet is a food that contains a protein source to which a dog has never been exposed, or one in which the proteins are broken down (hydrolyzed) into such tiny fragments that the body does not mount an allergic reaction against them. Elimination diets also typically contain either rice, which is rarely allergenic, or a novel source of carbohydrates (e.g., sweet potato).


It’s easy enough for a veterinarian to explain what’s involved in a food trial and sell owners an appropriate elimination diet or provide you with a recipe for a home-cooked version, but actually carrying the food trial out successfully at home is really hard. Invariably, I get calls from owners who say, "I just found out my father-in-law has been sneaking the dog steak," or, "My toddler keeps dropping her crackers on the floor, is that a problem?" The answer is, "Yes, it’s a big problem."


When the rules of the food trial are not strictly followed, it becomes very difficult to determine if a dog’s continuing symptoms are a result of the “extras” he’s been receiving or because he suffers from something other than a food allergy.


In human medicine, doctors sometimes employ a "patch test" to diagnose food allergies. A recent study looked into whether or not patch tests could be used in a similar manner in dogs and also evaluated the effectiveness of blood tests in diagnosing canine food allergies. I won’t saddle you with the results of the study’s statistical analyses (in truth, I don’t want to bone up again on the differences between sensitivity, specificity, and negative and positive predictability), but the paper’s authors concluded that “patch testing (and to a lesser degree serum testing) can be helpful in choosing ingredients for an elimination diet in a dog with suspected AFR [adverse food reaction]” but shouldn’t be used to diagnose the condition itself.


In other words, patch testing is better at telling you what a dog is NOT allergic to than if he is allergic in the first place, and if so, which foods are to blame.


Oh well. It looks like neither patch nor blood testing will replace the food trial any time soon. On the other hand, I can see a role for patch testing once a food allergy has been diagnosed. Many owners understandably do not want to go through the rigorous process of reintroducing ingredients one by one and monitoring for a return of symptoms to determine exactly what their dogs are allergic to, but they also do not like the idea of having to feed only the elimination diet used in the food trial for the rest of the pet’s life.


Patch testing could determine what ingredients are most likely to be safe, which would help guide decision making as to which new foods to try first.



Image: AVAVA / via Shutterstock

Comments  11

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  • Owner Compliance
    12/14/2012 12:06pm

    Do you find that owner compliance is one of the harder parts of veterinary practice?

  • 12/15/2012 09:06pm

    Yes, but I don't mean that in a bad way. I know first hand how hard it is to find the time, money, energy, what-have-you, to follow through on veterinary recommendations.

  • Patch Testing
    12/14/2012 05:27pm

    Patch Testing is done with raw proteins and therefore is often a wastd exercise.

    While I am not a proponent of feeding raw foods due to the risks of contamination for significant others in the household, just for starters, I myself was able to drink unpasteurized milk as a child and found as an adult that I have an intolerance to pasteurized protein in milk. It is not uncommon with allergies to find that what is fine when taken raw is an irritant when cooked, unfortunately.

    I have also noticed that each species seems to have its own worst offenders, which is logical as we are all built differently when it comes to enzymes and other metabolic tools.

  • But, dog food co's lie
    12/15/2012 03:00pm

    Elimination diets can be problematic when the dog food companies lie about the ingredients of their products. In a recent study by ELISA Technologies Inc., manufacturers of ten out of twenty-one tested commercial dog foods falsified the contents of their products by either including ingredients specifically excluded on the label or not including ingredients specifically advertised on the label. See http://cavalierhealth.org/blog.htm#September_27,_2012 for details.

    Home prepared meals are the answer, to this and so many other questions about our pets' overall health.

  • 09/27/2013 02:05pm

    Dry dog food manufacturers continue to lie about ingredients in their prescription allergen diets. http://www.cavalierhealth.org/diets.htm#Dry_dog_food_manufacturers_continue_to_lie_about_ingredients_in_their_prescription_allergen_diets

  • Problems with Allergies
    08/30/2013 01:35am

    My dog has been scratching and licking to the point where is is loosing hair, particularly on the legs. In addition she has no developed red spots on her belly. We have had her on two different limited ingredient foods over the past three 3 years. She is currently 3 and these problems developed around 2 or 2 1/2. We have also been to three different vets to try and resolve this issue. All three tested for mites, fleas, mange etc. etc. In the end all they could come up with is allergies and placed her on Benadryl which has shown no improvement. We have tried bathing her in medicated shampoos to help the itching, she has been on omega 3 but nothing seems to work. Does anyone have any advice?

  • 08/30/2013 07:10pm

    It sounds as if your best option is to make an appointment with a veterinary dermatologist. These specialists can usually get to the bottom of complicated skin cases that general practitioners cannot.

  • Allergy Testing
    09/25/2013 03:19pm

    I have recently heard about some allergy testing in Nampa, Id. It allows you to know what causes allergic reactions from what I understand. Have you heard anything this type of testing?

  • 09/26/2013 07:08pm

    Intradermal allergy testing or serum testing is notoriously unreliable in dogs. The elimination food trial is really the only way to go.

  • 09/26/2013 10:16pm

    It's my understanding that serum testing is also very unreliable for cats.

    However, I got really lucky years ago when my Ivy Elizabeth had lots of allergy problems. We tried all sorts of things and little Ivy got no relief.

    Even though I knew there was less than a 50% chance serum testing would provide answers, we did a R.A.S.T. test. The lab provided a list of all sorts of things to which Ivy was allergic (including kapok, chicken, all the dusts and molds and even cotton!) and put together injectable medication for her.

    It worked like a champ.

    I'll add that it ended up being fairly expensive, especially for a shot-in-the-dark test, but I've never regretted it. I doubt if anything would have helped since she was allergic to a variety of foods and materials.

    I guess the moral of the story is this: if you're willing to pay for testing that may or may not provide any help, I'd suggest trying it after trying diet alterations first.

  • 09/27/2013 01:59pm

    Ok, thanks for letting me know.




Photo of Jennifer

... graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999. In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado. She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms, Vet-Speak Deciphered for the Non-Veterinarian .

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics. Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.