It seems like a reasonable question.

After all, if blood tests can diagnose infections, hormonal diseases and many other conditions, surely there must be a blood test that tells us exactly what is causing a dog’s skin disease. The reality is more complicated. Perhaps the most important thing pet owners should understand is this:

Allergy blood tests do not diagnose allergic skin disease on their own.

That statement surprises many, but it is one of the most important principles in modern veterinary dermatology.

What Does an Allergy Blood Test Actually Measure?

Allergy blood tests measure allergen-specific antibodies produced against environmental allergens.

These allergens may include:

• House dust mites

• Storage mites

• Pollens

• Moulds

• Various environmental substances

The test identifies allergens that the immune system has recognised and produced antibodies against. However, recognition does not necessarily mean disease. Many perfectly healthy dogs with completely normal skin will test positive to environmental allergens despite showing no signs of itching or skin disease.

Why Can’t We Use the Test to Diagnose Allergies?

Because allergic skin disease is diagnosed clinically, not through laboratory testing alone. Veterinary dermatologists diagnose environmental allergic skin disease by evaluating:

• The patient’s history

• Age of onset

• Distribution of skin lesions

• Clinical signs

• Response to treatment

• Exclusion of other diseases

Before diagnosing environmental allergy, several other conditions must first be ruled out. These commonly include flea allergy dermatitis, ectoparasites such as sarcoptic mange, bacterial and yeast skin infections, and food allergy where appropriate. Only after these conditions have been appropriately investigated does environmental allergy become the most likely diagnosis.

The allergy test does not replace this diagnostic process.

A Positive Test Does Not Mean a Pet Is Allergic

This is where confusion often arises.

Imagine a dog that has no itching, no skin lesions and no history of allergic skin disease. That dog may still test positive to dust mites, pollens or moulds. The test tells us the immune system recognises those allergens. It does not tell us whether those allergens are actually responsible for causing disease.

What About Food Allergy Testing?

This is perhaps the most misunderstood area of all.

Blood tests marketed for food allergy diagnosis have not been shown to reliably diagnose food allergy in dogs. Research has consistently demonstrated poor accuracy and poor agreement with the results of properly performed dietary elimination trials. Hair tests, saliva tests and commercially available food allergy panels have similar limitations and should not be relied upon to diagnose food allergy.

The current gold standard remains a dietary elimination trial. While this process requires commitment and patience, it remains significantly more reliable than any available blood test.

So Why Do Dermatologists Use Allergy Testing?

Because allergy testing has a completely different purpose.

Once a dog has already been clinically diagnosed with environmental allergic skin disease, testing may help identify which allergens should be included in allergen-specific immunotherapy. This treatment is often referred to as Allergen-Specific Immunotherapy (ASIT) or allergy vaccines.

In this situation, the test is not being used to diagnose the disease.

The diagnosis has already been made.

The test is being used to formulate an individualised immunotherapy treatment. This is the critical distinction.

So When Is Allergy Testing Appropriate?

Allergy testing may be considered when allergen-specific immunotherapy is being planned. That’s it. And there are a few caveats.

Before testing is performed:

• A clinical diagnosis of atopic dermatitis should already have been established.

• Other common causes of itching, should have been investigated and excluded.

• Active skin infections, parasite infestations and significant disease flares should be appropriately controlled.

• Owners should understand that allergen-specific immunotherapy is a long-term treatment. Response is typically assessed after 9–12 months or longer, and many patients require lifelong therapy.

When Is Allergy Testing Not Appropriate?

Allergy testing is not recommended as:

• The first step in investigating an itchy dog.

• A substitute for a complete dermatological work-up.

• A method of diagnosing food allergy.

• A screening test in healthy animals.

Why a Structured Investigation Matters

Many skin diseases look remarkably similar. A dog with flea allergy dermatitis, food allergy, environmental allergy, bacterial pyoderma or yeast dermatitis may all present with itching and inflamed skin. The challenge is determining which disease, or combination of diseases, is actually responsible.

This requires a systematic, evidence-based approach rather than relying on a single laboratory test.

Successful dermatology is rarely about finding a quick answer. It is about asking the right questions, systematically ruling diseases in or out, and identifying the underlying cause before developing an appropriate long-term treatment plan.

The Bottom Line

Allergy blood tests are valuable tools, but they are often misunderstood.

They do not diagnose allergies.

They have low accuracy in determining food allergens.

They do not replace a thorough dermatological investigation.

Their primary role is to help identify allergens for allergen-specific immunotherapy after a clinical diagnosis of environmental allergic skin disease has already been established.

DermaVet TT
July 2026

References:

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2. Favrot, C., Steffan, J., Seewald, W. and Picco, F. (2010) ‘A prospective study on the clinical features of chronic canine atopic dermatitis and its diagnosis’, Veterinary Dermatology, 21(1), pp. 23–31.

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8. Mueller, R.S., Olivry, T. and Prélaud, P. (2015) ‘Critically appraised topic on adverse food reactions of companion animals (1): Duration of elimination diets’, BMC Veterinary Research, 11, Article 225.

9. Mueller, R.S., Olivry, T. and Prélaud, P. (2016) ‘Critically appraised topic on adverse food reactions of companion animals (2): Common food allergen sources in dogs and cats’, BMC Veterinary Research, 12, Article 9.

10. Nuttall, T., Marsella, R., Rosenbaum, M.R., Gonzales, A.J. and Fadok, V.A. (2019) ‘Update on pathogenesis, diagnosis, and treatment of atopic dermatitis in dogs’, Journal of the American Veterinary Medical Association, 254(11), pp. 1291–1300.

11. Olivry, T. and Mueller, R.S. (2017) ‘Critically appraised topic on adverse food reactions of companion animals (3): prevalence of cutaneous adverse food reactions in dogs and cats’, BMC Veterinary Research, 13(51), pp. 1–10.

12. Mueller, R.S. and Olivry, T. (2018) ‘Critically appraised topic on adverse food reactions of companion animals (6): prevalence of noncutaneous manifestations of adverse food reactions in dogs and cats’, BMC Veterinary Research, 14(341), pp. 1–5

13. Santoro, D., Marsella, R., Pucheu-Haston, C.M. and Eisenschenk, M.N.C. (2015) ‘Review: Pathogenesis of canine atopic dermatitis: Skin barrier and host–micro-organism interaction’, Veterinary Dermatology, 26(2), pp. 84–e25.

14. Steffan, J., Favrot, C. and Mueller, R.S. (2012) ‘A systematic review and meta-analysis of the efficacy of allergen-specific immunotherapy in dogs with atopic dermatitis’, Veterinary Dermatology, 23(6), pp. 451–e88.