Friday, January 15, 2021

About That Allergy Test - Blood/Hair/Saliva Tests for Dietary Sensitivity

     Many owners of itchy dogs are desperate for finding relief for their fuzzy companion. The red, irritated skin is painful to see, and managing allergies can be frustrating. It can feel like no matter what you try, nothing works! While the vast majority of canine allergies are environmental, it is common for people to seek out answers in dietary sensitivities-- primarily, with the use of an allergy panel that alleges to tell you every food item triggering your pup's scratching. However, these tests are a scam. After discussing why these tests are not worth the money, we will touch on why some people find success after running them.  

    When assessing a medical test, there are a handful of things to evaluate:

Sensitivity: This measures how often a test correctly identifies the thing that it is looking for, when that thing is actually there. In other words, a high sensitivity means a low rate of false negatives. 

Specificity: This measures how often a test identifies the thing that it is looking for, rather than something else. In other words, a high specificity means a low rate of false positives. 

Accuracy: This measures how close a test comes to the bullseye on average. 

Precision: This measures how close the results land to one another when repeated, regardless of whether it's on the bullseye or not. 


Time and time again, the canine food allergy tests available on the market have been shown to have low specificity (lots of false positives), low sensitivity (lots of false negatives), low to variable accuracy, and low precision. 

Here's the research:

"Can we diagnose adverse food reactions in dogs and cats with in vivo or in vitro tests?
(August 2017) - Review of 22 abstracts and articles on the subject. Authors found low repeatability and highly variable accuracy of the tests. Concluded the reliability was too low to recommend for diagnosis. 

"Testing for food-specific antibodies in saliva and blood of food allergic and healthy dogs"
(December 2018)
- Three groups of dogs, 11 with previously diagnosed and well-managed adverse food reactions, 15 dogs with atopic dermatitis undergoing elimination diet trials, and 16 clinically healthy dogs. These dogs had Hemopet Saliva tests done and Spectrum blood tests done. This study found that clinically healthy dogs tested 'positive' (falsely) for food allergies, and generally found low specificity and low sensitivity for testing of dogs with confirmed dietary allergies. Overall, authors concluded that these tests are not diagnostic and do not offer clinical insight for management of atopic dermatitis. 

"Hair and saliva analysis fails to accurately identify atopic dogs or differentiate real and fake samples"
(January 2019) -
 Three sample groups, seven fur/saliva samples from healthy animals, six from animals with atopic dermatitis, and eleven samples of synthetic fur and sterile saline. Samples were submitted twice for each participant. Positive results were received from all samples, including synthetic fur and sterile saline. Reproducibility between duplicate samples was the same as for random chance. Common triggers were identified between both live patient samples and synthetic fur/sterile saline samples. 

"Assessment of the clinical accuracy of serum and saliva assays for identification of adverse food reaction in dogs without clinical signs of disease"
(October 2019) -
 In survey and testing of 30 client owned animals, positive results were received for healthy animals with no history of allergic food reactions, and these results were not significantly correlated with prior exposure to certain foods. Authors do not recommend clinical use of these tests. 

Why these tests yield working results for some patients:

When told about these findings, many people's reaction is to recall their own success (or a friend's success) with managing their dog's allergies or sensitivities using the results of the panel they sent off. If you look back to the diagram above, the top left target board with low accuracy and low sensitivity has one dot in the bullseye area. Even if the results are completely random, occasionally they're bound to correctly identify something. The authors of the January 2019 paper above state why this is problematic very succinctly: "The promotion and marketing of unreliable health tests to consumers can result in real harm by delaying the time to correct diagnosis and institution of appropriate treatment. Additionally, results from such tests confuse the pet owner and veterinarian and use limited financial resources that could be better applied to appropriate testing and treatment." You may restrict certain items from your dog's diet that are not triggering allergies, or you may avoid certain items and continue to experience allergies! It can become very frustrating and it takes away time and money from getting a real, accurate diagnosis. 

How to identify diet allergies:

As mentioned above, dietary allergies and sensitivities are uncommon in dogs-- they represent only about 10% of dogs with allergies. Environmental allergies, such as to fleas, pollen, or dust, are far more common causes of skin irritation and itchiness. However, if your veterinarian has cause to believe your dog's symptoms may be from diet, there is only one way to diagnose it accurately: an elimination trial. In an elimination trial, your dog will eat a diet that should not cause any allergic reaction. That means the diet has to have no proteins that your dog has previously been exposed to, since previous exposure could result in a sensitivity developing. For that reason, many vets will recommend a hydrolyzed protein diet. These diets are only available with veterinary approval, and are made in such a way that the proteins are already broken down into pieces so small, your dog's immune system is unlikely to identify and attack them (the cause of allergies). This diet is fed for 8-12 weeks, exclusively, with nothing else offered by mouth (except water). If symptoms resolve, that suggests that the problem was dietary in nature, and you can then begin to 'challenge' ingredients one at a time, by re-introducing them to your dog's diet and monitoring for a reaction. This entire process should be done under the guidance of a veterinarian. Ideally, you would be seeing a specialist, either in dermatology or nutrition. 


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Additional Resources:

Research Update: Testing for Food Allergies - Tufts Vet Nutrition

Figuring Out Food Sensitivities - Tufts Vet Nutrition

Chances Are Its Not a Food Allergy for Your Dog - TuftsYourDog

Is there a gold-standard test for adverse food reactions?

Feeding Raven Doodles - Food Allergies