Let's jump right in with a recent research study by Bernstein et al. (2019), entitled: "Hair and saliva analysis fails to accurately identify atopic dogs or differentiate real and fake samples".
You can probably see where this post is headed, just from reading the title above. We are often asked to formulate diets for pets based on the results of hair, blood or saliva allergen testing, and it's quite frustrating, for a number of reasons. Most of all, I don't like to see pet owners waste their money on dubious testing, but I also hate to see pets on very limited diets when this is completely unnecessary.
As part of the study above, the authors submitted hair and saliva samples from both healthy dogs and dogs with atopic dermatitis, and submitted them for analysis by a popular commercial direct-to-consumer hair and saliva allergen testing company. The really entertaining part - they also submitted fake hair samples (synthetic fur), and sterile saline, instead of saliva.
What they found was that the company offering the allergen testing provided positive results for all samples, including the fake fur and saliva samples. What this means is that they identified "allergens" for samples that weren't even biological in origin. The authors state: "The test results for healthy and atopic animal samples were no different from each other or from synthetic fur and saline samples. Reproducibility for paired samples was not different from random chance. The results for real animals correlated strongly with results for synthetic fur and saline samples."
Pretty disappointing, right?
A second study, by Coyner and Schick (2019), confirmed very similar results. These authors also submitted samples from a healthy dog, a dog with diagnosed allergies, and fake fur and saliva samples, to determine whether "the test could differentiate between a real dog and toy animal". As per above, the results were not different from that expected due to random chance.
What about a blood test for allergies? Udraite et al. (2019) looked at the accuracy of an ELISA serum test for food-specific IgE as part of their research, and found that sensitivity, positive predictive value and likelihood ratio, specificity, negative predictive value and likelihood ratios were unsatisfactory. There was no clear difference in the number of positive reactions between the allergic dogs and healthy dogs. This study was well-designed, because they actually used an elimination diet, followed by re-challenge with specific foods, to properly identify allergens in the study population, so they did have reliable information to compare with their test results.
If you need any more convincing, consider that, in humans, more than 50 percent of all blood tests for food allergens will yield a “false positive” result. This means that the test yields a positive result, even though the patient is not allergic to the food being tested. This can happen because the test can sometimes measure a response to undigested food proteins, or because the test may be detecting proteins that are similar among different foods (for example, chicken and duck) but these detected proteins do not trigger allergic reactions (cross-reactivity).
So what should you do to find out if your pet has food allergies? The gold standard is still an elimination diet trial, which your vet can help you do. This involves feeding your pet a commercial hydrolysed diet, or a homemade novel protein diet, for 2-3 months, to see if clinical signs (usually skin or gastrointestinal signs) improve. If they do, a food allergy is likely. Challenging with different proteins is the next step, in order to try and identify what's causing the problem. We have an upcoming post on novel protein diets, so I won't go into detail about this - but they remain a sound approach to diagnosing food allergies.
So please - don't waste time and money on hair, saliva or blood tests for food allergies - these tests are inaccurate and unreliable.
Read the Udraite et al. (2019) paper here: https://pubmed.ncbi.nlm.nih.gov/30819419/
Read the Coyner and Schick (2019) paper here: https://pubmed.ncbi.nlm.nih.gov/30371955/
Read the Bernstein et al. (2019) paper here: https://pubmed.ncbi.nlm.nih.gov/30680834/