Allergy Testing in Canine Atopic Dermatitis: When Is It Really Necessary?

When a dog presents with chronic pruritus, one of the most common requests from pet owners is, “Can we do an allergy test?” While allergy testing is often viewed as the key to diagnosing canine atopic dermatitis (CAD), this is one of the most persistent misconceptions in veterinary dermatology. 

In reality, CAD is a clinical diagnosis, and allergy testing plays a very different role: it helps identify environmental allergens for allergen-specific immunotherapy (ASIT) rather than confirming the disease itself¹. Understanding when and why to test is essential for appropriate case selection and effective long-term management. 

CAD Must Be Diagnosed Before Any Testing 

Before considering allergy testing, CAD must be established through a structured diagnostic approach. 

This includes: 

• Detailed clinical history 

• Characteristic lesion distribution 

• Exclusion of ectoparasites 

• Identification and treatment of secondary infections 

• Elimination diet trial to rule out food allergy 

• Application of Favrot’s criteria¹ 

Only after these steps is CAD diagnosed with confidence. 

A key principle: 

A positive allergy test does not diagnose CAD.  

What Allergy Testing Actually Measures 

Allergy testing identifies IgE-mediated sensitisation, not clinical disease. 

When an allergen binds to allergen-specific IgE on mast cells, it triggers mast cell degranulation and the release of histamine and other mediators, producing an immediate wheal-and-flare response². This reaction demonstrates that the immune system has been sensitised to an allergen, but it does not confirm that the allergen is responsible for clinical signs. 

This distinction is critical: 

Sensitisation is not equal to clinical allergy. 

Many dogs may test positive to environmental allergens simply due to exposure without clinically relevant disease^1,2. 

When Should Allergy Testing Be Performed? 

Allergy testing becomes useful only after CAD has been diagnosed and the goal shifts toward long-term disease modification. 

It is recommended in dogs that: 

• Have moderate to severe CAD 

• Show recurrent or year-round clinical signs 

• Require long-term anti-pruritic therapy 

• Have inadequate disease control with standard management 

• Are candidates for allergen-specific immunotherapy (ASIT) 

• Have owners seeking a disease-modifying approach rather than lifelong symptomatic control¹ 

In contrast, testing is not useful in dogs with mild, seasonal, or well-controlled disease. 

Intradermal Testing vs Serum IgE Testing 

Two main methods are used to identify environmental allergens for ASIT. 

Intradermal Testing (IDT) 

IDT evaluates the skin’s immediate hypersensitivity response to injected allergens and is widely used in veterinary dermatology. 

Advantages: 

• Direct assessment of cutaneous response 

• Long-established clinical utility 

• Useful for selecting allergens for immunotherapy 

Limitations: 

• Requires sedation in most cases 

• Drug withdrawal is necessary 

• Requires specialised expertise^1,3 

Serum Allergen-Specific IgE Testing 

This test measures circulating allergen-specific IgE antibodies from a blood sample. 

Advantages: 

• Easy sample collection 

• No sedation required 

• Widely available 

Limitations: 

• Variability between laboratories 

• Positive results may reflect exposure rather than disease relevance 

• Results must always be interpreted in context^1,3 

Importantly, agreement between serum IgE and IDT is not always consistent because they evaluate different aspects of the allergic response. Neither test should be interpreted in isolation. 

What About Skin Prick Testing? 

In human medicine, the skin prick test (SPT) is the preferred first-line diagnostic tool for IgE-mediated allergic diseases because it is rapid, inexpensive, highly specific, and does not require sedation.⁴ The reaction is observed within minutes and reflects immediate hypersensitivity mediated by mast cell degranulation. 

Interest in adapting SPT for dogs has increased in recent years. Early studies suggest that SPT may detect allergen sensitisation in dogs with clinical signs compatible with CAD, with high specificity reported under controlled conditions². However, variability in allergen extracts, lack of standardisation, and moderate sensitivity currently limit its routine clinical use in veterinary practice. 

At present, SPT remains investigational in dogs, and IDT and serum IgE testing remain the recommended methods for selecting allergens for immunotherapy^1,3,4. 

Common Mistakes in Allergy Testing 

Misinterpretation of allergy testing results is common and can lead to inappropriate management. 

Frequent errors include: 

• Using allergy testing to diagnose CAD 

• Skipping elimination diet trials before testing 

• Interpreting every positive result as clinically relevant 

• Ignoring seasonal or geographic context 

• Initiating immunotherapy based solely on test results 

• Testing clinically unstable patients 

A positive result only confirms sensitisation—it does not confirm disease causation^1,2. 

Preparing the Patient for Accurate Results 

For best results: 

• Treat secondary infections before testing 

• Stabilise pruritus where possible 

• Follow medication withdrawal guidelines 

• Ensure clinical disease is controlled enough for interpretation 

These steps reduce false positives and improve allergen selection accuracy for ASIT. 

Where Allergy Testing Fits in ASIT 

Allergen-specific immunotherapy remains the only treatment capable of modifying the course of CAD by retraining the immune system to tolerate environmental allergens. 

However, the success of ASIT depends heavily on appropriate allergen selection, which is why testing is performed only after diagnosis—not before¹. 

The Clinical Take-Home 

Allergy testing is not a diagnostic tool for canine atopic dermatitis. It is a targeted investigation used to identify clinically relevant environmental allergens once CAD has already been diagnosed. Intradermal testing and serum IgE testing remain the established methods for guiding allergen-specific immunotherapy, while emerging techniques such as skin prick testing show promise but are not yet part of routine veterinary practice. The key clinical principle remains unchanged: diagnose the disease first, then use allergy testing to individualise long-term management. 

References (Vancouver) 

1. Outerbridge CA, Jordan TJM. Current knowledge on canine atopic dermatitis: Pathogenesis and treatment. Adv Small Anim Care. 2021;2:101–115. doi:10.1016/j.yasa.2021.07.004. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC9204668/ 

2. Carmona-Gil AM, Sánchez J, Maldonado-Estrada J. Evaluation of skin prick-test reactions for allergic sensitization in dogs with clinical symptoms compatible with atopic dermatitis. A pilot study. Frontiers in veterinary science. 2019 Dec 17;6:448. https://doi.org/10.3389/fvets.2019.00448

3. Hensel P, Santoro D, Favrot C, Hill P, Griffin C. Canine atopic dermatitis: Detailed guidelines for diagnosis and allergen identification. BMC Vet Res. 2015;11:196. doi:10.1186/s12917-015-0515-5. https://bmcvetres.biomedcentral.com/articles/10.1186/s12917-015-0515-5 

4. Olivry T, DeBoer DJ, Favrot C, Jackson HA, Mueller RS, Nuttall T, Prélaud P; ICADA. Treatment of canine atopic dermatitis: Updated guidelines. BMC Vet Res. 2015;11:210. doi:10.1186/s12917-015-0514-6. https://bmcvetres.biomedcentral.com/articles/10.1186/s12917-015-0514-6