Should My Vet Test My Dog And Cat For Allergies?

Should My Vet Test My Dog And Cat For Allergies?

Ron Hines DVM PhD



NexGard®, Bravecto®, Simparica®?

Atopica® My Cat?

  Atopica® My Dog? 

 Redonyl Ultra?

Skin allergies and itching (canine atopy) are the second most common reason pet owners bring their dogs to veterinarians (ear infections are the 1st). It’s the 7th most common complaint from cat clients. And if you consider that ear infections and hot spots are often due to underlying allergies, allergic problems are the number one reason dog’s come to visit me. 

I live with my  allergic dog, Maxx, whom I love dearly. So I am on both the giving and the receiving end of my own advice. When you are dealing with allergic pets, you have a limited number of options: You can treat your pet with soothing lotions and shampoos, you can give them medications that suppress their immune system (corticosteroids, Atopica® , Apoquel® or Cytopoint® ) or you can attempt to have the things your pet is allergic to identified and see if periodic allergy shots and/or avoidance might help them (hyposensitization=desensitization injections). Veterinarians like myself will send you home with other things – antibiotics, fatty acid supplements, antihistamines, tranquilizers, special diets, etc. All of those products can be helpful but are time consuming and give less than spectacular results.

Most dog and cat owners know about the potent side effects of long term use of powerful drugs like steroids and Atopica® (cyclosporin) – so allergy testing, desensitization or avoidance can be quite appealing. It is certainly a procedure with little or no downside – other than the expense and time. 


Skin Tests To Find Out What My Dog Or Cat Is Allergic To

Human and veterinary dermatologists still rely on skin testing, a time-honored procedure in which a small amounts of the things (allergens) that dogs and cats commonly become allergic to are injected or scratched into the deeper layers of your pet’s skin. It is an exacting, expensive and time-consuming procedure. Results can also “straddle the fence” and be quite difficult to interpret. We call this an in vivo test because it duplicates (as best we can) the things that happen in allergic dogs and cats when they inhale or come in contact with an offending allergen. All the resources and defenses that your pet’s immune system would use to destroy the particular antigen(s) (= degranulation) come into play. In that process, redness and swelling at the injection sites represent a positive test result. Most dermatology experts believe that skin test panels such as I just described are the only accurate method of detecting allergies with any confidence ( the closest thing we have to a “gold standard”).

Skin tests to determine what your pet might be allergic to are considerably more accurate, on the whole, than blood tests. However, they are not 100% accurate either. To have them performed, you will need to locate a board certified veterinary dermatologist. The test requires only mild sedation. A patch of hair will be shaven from your pets rib cage area and a patchwork of injections will deposit small samples of the most common offending allergens in your area into the pet’s skin. When it is performed, your pet might look like the photo above. Veterinary dermatologists often state that 50-60% of pets are commonly said to benefit from periodic injections of the extracts prepared according to their skin test results. In dogs, as in humans, exposure to inhaled allergies runs in families. No scientific studies on success rates have been run in dogs or cats, but in humans it ran from 38-54% in one study regarding hay fever. (read here)   In a study regarding the effectiveness of desensitization shots in treating allergic asthma, the effectiveness was 0%. (read here)  Others found “marginal benefits”. (read here) Unfortunately, almost all published studies on the effectiveness of desensitization shots or oral desensitization drops in animals and humans are industry-supported or industry-generated.

What About Blood-based Tests Available At My Local Animal Hospital?

Because of the expense and specialized training needed to perform and interpret skin tests, veterinarians and pharmaceutical supply houses have always been on the lookout for simpler and cheaper procedures – ones that ordinary veterinarians can perform in their offices without the need of a trained specialist and loss of their clients. These blood-based antibody tests have come on the market several times, in the past. Currently Heska Corporation make markets their Allercept® blood IgE allergy test (along with custom prepared desensitization shots or oral desensitization drops) . The VCA animal hospital chain, a division of the Mars Confectionery Company markets their own . Idexx Laboratories has their version too . These tests all rely on detecting the presence of antibodies called IgE that allergic pets (and humans) produce against things they have become allergic to. There are approximately 500 different allergen substances now available commercially to test for the presence of individual IgE levels in your dog or cat’s blood specifically against each one.  Specific Ig molecule classes are generated in the billions and each class is different enough from the others (with exceptions) so that it can trigger an allergic response the the specific antigen that prompted its formation. (read here)

IgE antibodies are produced by a special group of your dog and cat’s lymphocytes called  plasma cells . Some call this their “gate keeper function” . The itchy inflammatory process in your pet’s skin that is begun by a specific IgE is extremely complex, involves many biochemical participants and not fully understood.

Are You Hesitant About The Value Of These Blood Tests?


I am quite confident that all these tests accurately measure the levels of IgE in your pets’ blood. But it is much less certain that knowing these specific IgE levels will help your pet. In a German study that checked these blood-based allergy tests for accuracy in determining which dogs had food allergies the results were unreliable. (read here). A Louisiana study, determining the accuracy of these test (RAST tests) found them to be highly inaccurate. (read here).  An Austrian study found that not only were these test inaccurate, they made mistakes as to which individual IgE class antibodies were directed against. That is because some IgE classes cross-react with several different antigens (CCDs). (read here) Blood-based allergy tests are notoriously inaccurate. For instance, about 1/3 of people with allergies to grass pollen also came out IgE blood test positive for being allergic to peanuts but had negative skin test results for a peanut allergy. (read here) . The veterinary school in Queensland, Australia performed a study using the Allercept® test on West Highland Whites. They compared the IgE test results of normal Westies to the results of itchy Westies. They found that normal Westies actually had higher levels of specific IgE than the itchy (Atopic) ones. (read here) A study at the veterinary school in Illinois was equally negative regarding the use of blood allergy tests. Their conclusion was that “the ability to make clinical determinations of significance was marginal ” (read here) An Edinburgh, Scotland study came to a similar conclusion that IgE measurements were valueless – normal, non-itchy dogs has as much circulating IgE as itchy ones. They remarked in their conclusion: that there is a high incidence of positive IgE and intradermal skin test results in non-allergic, normal dogs. (read here)  

The Mayo Clinic, on its website, suggests blood-based allergy tests only as a last option for patients who have such severe and extensive skin allergy rashes that a dermatologist would have difficulty interpreting skin tests results, or when discontinuing the anti-itch medications the patients must take would be dangerous (many of those meds invalidate skin test results). The Mayo Clinic ended by remind physicians of the “limited sensitivity” of blood-based allergy tests in general. 

the companies like Heska, VCA and Idexx marketing these blood test to veterinarians and pet owners all claim to have performed in-house (internal) studies that show that their tests work. They send their representatives to veterinary conventions to tout the benefits of their blood-based allergy tests, advertise heavily in veterinary publications and offer state-required CE credits to veterinarians who will sit through their online sales pitches. But the study they have not done tell us the most. They have not determined that the levels of class-specific blood IgEs in dogs and cats that remained healthy (the ones that don’t have itchy skin) are any lower than the levels in dogs and cats that itch. They also have not conducted studies to show that class-specific IgEs don’t react to more than one antigen. It is commonly known that that occurs. Until they do run those tests I am going to remain quite skeptical as to the value of the blood tests they sell. We really don’t know if high IgE levels to a particular antigen mean anything that is relevant to your dog or cat’s itching and general health. 

Proving that a treatment benefits an itchy dog or cat can be very difficult. We all know that pets have their good days and their bad days. You also know that itching problem can be seasonal or related to boredom, stress and breed. On top of that, realistic veterinary dermatologists will tell you that they strive for modest allergy improvements – not cures. With such a hazy target, you can see why the benefits of allergy blood tests like these and the desensitization treatments they eventually lead to can be very hard to judge. 

What About Allergic Cats?

Much less is known about allergic cats. The only study that I know of that compared the test results of allergic cats to test results of non-allergic cats found no difference between the number of cats that had high specific IgE levels in either group when measured with the Heska Allercept® method. (read here)

Should I Have This Test Performed Or Not?

Veterinarians like myself are always in a quandary when dealing with allergic pets. The products that actually work all have the potential for serious side effects. When we give those drugs, we give them as sparingly as we can and we feel better doing so when we know that we have exhausted every other option. That is why I still encourage a few of my clients to have these tests run before resorting to the long term use of powerful medication. Perhaps these tests will benefit your pet. I would be quite happy if all the articles I linked you to were wrong. If the allergy blood tests and desensitization based on the test results don’t really work, at least you and I will feel better knowing that we did everything in our power to avoid a lifetime on powerful medications. But I want you to understand the major limitations of these blood tests before you pin your hopes on them. I also have a concern that “desensitizing” your pet to a cocktail of allergen that your dog or cat is not really allergic to might actually make the pet allergic to those antigens after years of repeated “desensitizing” injections. 

What About Blood Tests For Food Allergies?

Most veterinarians believe that the majority of itchy pets with allergic dermatitis (canine & feline atopy) develop their problem due to things they inhale or that come in contact with their skin (such as fleas) – not the things they eat. But we know that some pets (perhaps 10-15%) do become itchy due to allergies to things in food. (read here) Most of the laboratories that offer blood tests for things like dust mite and flea allergies also offer panels for dog and cat allergies to food ingredients. Those tests are also highly inaccurate. Just like the blood panels for inhalant allergies, a negative test result might be of some value in planning your pet’s diet. But a positive test is as likely to be a false-positive as a true-positive. Studies have found that these tests are really not worth performing. (read here) You have a much better option than blood tests: Put your pet for two-month on a test diet and see if it improves. Most authorities do not wait that long. They make their judgment after a single month. I would have patience and give the test diet a bit longer. You have several options, you can purchase a commercial diet that has been processed to make its ingredients hypo-allergenic (the ingredients in them are heated to hydrolyze them). These are diets like Purina’s H/A™ , Hills Z/D™  or Royal Canin’s HP™I suggest you only use these diets for two months to see if food ingredients are really the cause of your dog or cat’s problem. Then prepare a diet at home from novel ingredients that your dog or cat has never eaten before. HA is a no-meat vegetarian formula. I am not a fan of vegetarian diets for dogs or cats. Read about that here. You will find some suggestions on preparing your pet’s food at home  here . Some of those are actually based on recipes Hills once distributed to veterinarians. The internet is also full of other dog and cat diet recipes. It is always wise to have an online veterinary nutritionists supply or review the recipes you prepare for your pet at home. Remember, dogs on a test diet must consume nothing besides those low-antigen or novel antigen ingredient diets if the test results you obtain are to have meaning. Just like skin testing, the less medications your pet consumes prior to testing, the better.

What Does The Future Hold?

There probably will come a time when allergy testing gives results that are useful. I have my hopes pinned on basophil activation tests.

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