So You Think Your Dog Has Allergies, Part 2: Diagnosis

In my last post, I discussed the types of allergies dogs typically have- flea, environmental, and food- as well as the typical symptoms. These symptoms can range from irritating to painful for your dog, so it’s important that you treat them. That said, it is tricky to treat them if you don’t know what they are, so today’s post will discuss some ways you can determine what your dog’s allergies are.

The first step in diagnosing allergies is to visit your vet to rule out other health problems. There are a number of other issues that can mimic the itching typical of allergies (and the not-so-typical symptoms like GI distress).

Veterinary Tests
Your vet can perform a few tests to determine what your dog is allergic to. There are two basic types that I’m aware of: a blood test that can detect antibody levels, and a skin or intradermal test.

Blood tests are relatively simple; your vet simply draws a vial or two of blood and sends it into a lab to be analyzed. The Whole Dog Journal’s April 2011 article Itching to be Well recommends doing the blood test at the end of peak allergy season- typically the fall in North America- as this is when antibody levels are highest. There will probably be some false positives or negatives, which means that while this test can be helpful, it may get some things wrong.

The skin/intradermal test requires shaving your dog’s belly/side, injecting small amounts of various allergens, and then reading the reaction. It is more time consuming, expensive, and stressful for your dog, but it is also more accurate.

It should be noted that neither test is very reliable for foods- the Whole Dog Journal article cites a 30% accuracy rate- so take those results with a grain of salt. The best way to test your dog for food allergies is through the use of a food elimination trial.

Food Elimination Trials

This is what I feed now, but look at the ingredients below; 

despite the high quality, it's entirely inappropriate for a food elimination trial.

When you do a food elimination trial, you feed your dog a diet with one protein source, and one carbohydrate source, and nothing else. Both the protein and carb should be novel- something you’ve never fed before. With the explosion in the pet food market, it is getting more difficult to do this. Some of the proteins that used to be recommended- like lamb and duck- are pretty standard now days.

It’s the “nothing else” that’s even trickier, though, because everything you feed your dog- from food to treats to chewies- needs to be of either that protein or that carb, and you’ll need to be vigilant to make sure he doesn’t sneak any scraps, or mug a friendly pet store clerk for treats.

I personally recommend using a fresh, homemade (raw or cooked) diet during this time. It will not be a balanced diet, but if your dog has previously had good nutrition, it is highly unlikely any nutritional deficiencies will show up during the relatively short period you'll need for testing. The problem with using kibble is that there are just so many ingredients in them, and your dog might be allergic to any of them.

If you really want to use kibble, feeding a prescription diet for allergies is probably your best bet. These diets typically work by using hydrolyzed proteins, which are proteins that have been broken down molecularly so they are so small that the dog’s body shouldn't react to it. As a side note, don't be fooled by packages that claim to be limited ingredient diets or hypoallergenic. You will need to read the labels for yourself to see exactly what's in that food. 

No matter what you choose to feed, you must feed it exclusively for a minimum of 8 to 12 weeks. This allows your dog’s body to rid itself of the histamines from previous foods that might have been causing a problem. If, at the end of this time, your dog is still itchy, you can conclude one of two things: either your dog’s itchiness is not due to food, or you had the spectacularly bad luck to choose a food that your dog was allergic to. I’ve even heard of some rare cases where a dog has reacted to hydrolyzed protein diets. Switch diets and try again, waiting for 8 to 12 weeks before moving to the next step.

Food Challenge
Simply feeding the elimination diet is only half the task, though. Now you must challenge your dog’s diet. It is important that you continue to feed nothing but the novel protein and carb, however, you will add one single food to your dog’s diet for one week. If your dog is allergic to the new item you’ve added, you’ll probably see the recurrence of symptoms within a week, and sometimes sooner.

If your dog is still itch-free at the end of the week, you can safely assume your dog is not allergic to that item. Continue to add a single item at a time weekly, taking note of what causes your dog to react, and what doesn’t. Soon, you should have a list of your dog’s food allergies.

Keep Notes!
Of course, it’s always possible that you’ll introduce a new food item at the same time your dog is exposed to fleas or mold or pollen. That’s why simply keeping a log of your dog’s symptoms, noting if there is any correlation with potential allergens, can be very helpful. Weather.com has an app you can use to determine different pollen levels in your area each day. Make a note of which ones are displayed on days your dog is itchy. Over time you might start to see some trends.

My Experiences
I spent close to six months trying different foods with Maisy. She remained itchy for most of the trial, although she did react quite strongly when we tried a lamb-based kibble. Ultimately, I got so frustrated that I had the blood test done (it was January in Minnesota, so my vet did not want to have to shave her belly for the intradermal).

The results showed that Maisy is allergic to both lamb (which I’d already figured out) and eggs (which I’ve subsequently tested and confirmed), as well as a variety of grasses, trees, weeds, wool, mold, and the mind-boggling human dander. Although it is quite possible that there were some errors or omissions (remember, the blood test is prone to false positives and negatives), this got us close enough. Despite the poor accuracy rate for food allergies, they proved to be correct for us. Since Maisy’s allergies are fairly mild, our treatment course was the same, regardless of whether or not every single environmental item was accounted for.


But we’ll talk about treatments in the next post. For now, I’d love to hear about your experiences diagnosing your dog’s allergies. How did you do it? Was it frustrating… or easy? Would you do anything differently? And what is your dog allergic to? Comment below!