How Does Dog Allergy Testing Work?

By Dial A Vet Veterinary Team

If your dog is itchy year after year, an allergy test sounds like the obvious way to get an answer. Many owners are surprised to learn that allergy tests cannot tell whether a dog has allergies in the first place. That diagnosis comes from history, examination and ruling out other causes. What testing does well is identify which environmental allergens to target once a vet has already decided your dog has atopic dermatitis, usually so they can make a custom immunotherapy treatment.

Key takeaways

• Allergies in dogs are diagnosed clinically, by ruling out other itchy conditions. Tests do not make the diagnosis.
• Intradermal skin testing and blood (serum IgE) testing identify environmental allergens such as pollens, grasses, dust mites and moulds.
• Test results are mainly used to formulate allergen immunotherapy (allergy shots or drops).
• Food allergies cannot be reliably diagnosed with blood, hair or saliva tests. An elimination diet trial is the only reliable method.
• Home hair and saliva allergy kits sold online are not scientifically validated.

The three types of allergy in dogs

• Flea allergy dermatitis: a reaction to flea saliva. Very common in Australia and the first thing to rule out.
• Food allergy (adverse food reaction): usually to a protein such as beef, chicken, dairy or wheat.
• Atopic dermatitis: an allergic reaction to environmental allergens such as grass and tree pollens, house dust mites and moulds. In Australia, grasses such as couch, kikuyu and paspalum, along with house dust mites, are common culprits.

Many dogs have more than one, which is part of why diagnosis takes patience.

How vets diagnose allergies first

Before any test, your vet will work through other causes of itch:

1. Fleas: strict flea control on every pet in the household for at least two to three months.
2. Mites: skin scrapings, and often a treatment trial for sarcoptic mange.
3. Infections: skin cytology to check for bacterial and yeast infections, which are treated before going further.
4. Food allergy: an elimination diet trial.

If your dog is still itchy after all that, with the right pattern of signs (paws, face, ears, armpits, belly, often starting between six months and three years of age), the diagnosis is atopic dermatitis. Only then does allergy testing become useful.

Intradermal skin testing

Considered the reference method, this is usually performed by a veterinary dermatologist.

• Your dog is lightly sedated and a patch of fur is clipped on the side of the chest.
• Tiny amounts of many different allergens are injected just under the skin in a grid pattern.
• After about 15 to 20 minutes, the vet looks for raised, red bumps where your dog's immune system has reacted.
• Some medications, especially steroids and antihistamines, need to be stopped for a period beforehand because they can block reactions. Your vet will advise exactly how long.

Blood (serum IgE) testing

• A blood sample is sent to a laboratory to measure allergen-specific antibodies.
• It can be done at a general vet clinic, without clipping or sedation.
• It is less affected by some medications than skin testing.
• It can produce false positives, which is why results must be interpreted alongside your dog's history.

Some dermatologists use both tests together to build the most accurate picture.

What about food allergy tests?

Blood tests for food allergy, as well as hair and saliva tests, have been studied repeatedly and do not reliably identify food allergies in dogs. One study even submitted fake samples (synthetic fur and water) to commercial hair and saliva tests and got "positive" results.

The only reliable way to diagnose food allergy is an elimination diet trial:

• Your dog eats a prescription hydrolysed diet, or a novel protein diet chosen with your vet, and nothing else for about eight weeks.
• No treats, flavoured medicines, chews, table scraps or other food.
• If the itch improves, the original food is reintroduced. A flare within days to two weeks confirms the allergy.

Our article on food allergies in dogs explains this in more detail.

What happens after testing

Results are used to create allergen-specific immunotherapy, a custom vaccine made for your dog given as injections under the skin or as drops under the tongue. It slowly retrains the immune system to tolerate the allergens. Around 60 to 70 percent of dogs show useful improvement, but it often takes six to twelve months to see the full effect. Many dogs also continue other treatments, such as medicated shampoos and anti-itch medication, in the meantime.

Testing also gives practical knowledge. If your dog reacts strongly to house dust mites, for example, regular hot washing of bedding may help.

Is allergy testing worth it?

It is most worthwhile if:

• Your dog has confirmed atopic dermatitis
• The itch lasts more than a few months each year
• You are interested in immunotherapy, which targets the cause rather than just the itch
• Other treatments have side effects or are not giving good control

It is less useful if your dog has only mild, seasonal itch well controlled by other means.

FAQ

Can my regular vet do allergy testing?
Most general vets can collect blood for serum testing. Intradermal skin testing is usually done by a veterinary dermatologist.

Are hair and saliva tests from the internet accurate?
No. They are not validated and can give misleading results, sometimes leading to unnecessary diet changes.

How old does my dog need to be for testing?
There is no strict age limit, but most dogs are tested after at least one full allergy season so results reflect real exposure.

Will my dog be cured by immunotherapy?
It rarely cures allergy completely, but many dogs need less medication and itch much less.

Talk with a vet

If your dog has been itchy for a long time, a Dial A Vet veterinarian can help you understand where allergy testing fits, what to rule out first and whether a dermatology referral makes sense. Book a Dial A Vet consult. See also our guide to itch relief for dogs.

References

• Hensel P, Santoro D, Favrot C, Hill P, Griffin C. Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification. BMC Veterinary Research. 2015;11:196.
• Mueller RS, Olivry T. Critically appraised topic on adverse food reactions of companion animals (4): can we diagnose adverse food reactions in dogs and cats with in vivo or in vitro tests? BMC Veterinary Research. 2017;13:275.
• Coyner K, Schick A. Hair and saliva test fails to identify allergies in dogs. Journal of Small Animal Practice. 2019;60(2):121-125.
• Olivry T, DeBoer DJ, Favrot C, et al. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA). BMC Veterinary Research. 2015;11:210.

Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.