Allergy Skin Testing vs. Serology Blood Testing in Equine Patients

Allergic skin diseases in horses can be challenging to diagnose and manage. Over recent years, allergy diagnostic tools have improved significantly, allowing veterinarians to identify allergens more precisely. However, despite these advances, Allergy Skin Testing (Intradermal Skin Testing, IDST) remains the gold standard for diagnosing equine allergies. Many horse owners and veterinarians are familiar with serology testing—a blood test often performed through commercial labs — but this method to date has important limitations that impact its reliability.

This blog post aims to clarify why Allergy Skin Testing is preferred by dermatology specialists, explain the pitfalls of serology testing, and emphasize the unique need for specialized veterinary dermatology care when managing equine allergies.

Understanding Allergy Skin Testing (IDST)

How It Works

Allergy Skin Testing involves injecting tiny amounts (0.1ml) of suspected allergens into the skin, usually on the neck or chest area. After about 15–20 minutes, the injection sites are evaluated for size, swelling, and redness, which indicates a hypersensitivity reaction. This method measures the immediate hypersensitivity (Type I) immune response mediated by mast cells releasing histamine in the skin.

Advantages of Skin Testing

• Direct measurement of clinical hypersensitivity: The test assesses how the horse’s skin reacts in real time to each allergen.

• High sensitivity and specificity: Because allergens are introduced in their natural form and tested in vivo, the results closely reflect the horse’s true allergic status.

• Better correlation with clinical signs: Positive reactions often correspond to actual environmental exposures relevant to the horse’s symptoms.

• Guides targeted immunotherapy: Knowing exactly which allergens cause reactions helps tailor allergy shots or avoidance strategies.

Serology Testing: What It Is and Its Limitations

What Serology Testing Measures

 Serology testing analyzes the horse’s blood serum to detect IgE antibodies specific to various allergens. These tests are easier to perform since they only require a blood draw and can screen many allergens simultaneously.

The Problem of Anti-CCD IgE Antibodies

 A critical limitation of serology in horses is the interference caused by anti-CCD IgE antibodies:

CCDs (Cross-reactive Carbohydrate Determinants) are carbohydrate molecules present on many allergen proteins. Horses often produce IgE antibodies that bind to CCDs rather than the protein parts of allergens. This binding causes false-positive reactions on serology tests because the test detects IgE binding to CCDs rather than true allergen sensitization. The result is polysensitization, where the test indicates allergies to multiple unrelated allergens.

Consequences of False Positives

• Leads to misleading diagnoses.

• May cause veterinarians to prescribe overly broad or inappropriate immunotherapy.

• Increases treatment costs and prolongs ineffective management.

• Can frustrate owners, drive up costs, and delay effective relief for the horse.

The Importance of Specialized Veterinary Dermatology Care

Equine dermatology is a niche field with few specialists nationwide. Many practicing equine veterinarians manage allergic skin diseases without access to advanced diagnostic tools or specialized training in allergy management.  Well over 90% of our equine dermatology patients arrive as referrals after such experiences, seeking specialized care after months or years of unsuccessful management.  Some of these referrals are even equine vets themselves

Consulting a veterinary dermatologist experienced in equine allergies offers several benefits:

• Access to precise diagnostic methods like IDST.

• -Expert interpretation of complex allergy test results.

• Development of targeted immunotherapy plans.

• Improved treatment outcomes and faster relief for patients.

Summary Table: Allergy Skin Testing vs. Serology Testing in Horses

References:

- Marsella R., et al. "Comparison of Intradermal Skin Testing and Serum Allergen-Specific IgE Levels in Horses with Atopic Dermatitis." Veterinary Dermatology, 24(1): 45-52.

- May K., et al. "Evaluation of Serum Allergen-Specific IgE Tests for Allergic Diseases in Horses." Equine Veterinary Journal, 35(4): 354-360.

- Nuttall T., et al. "Assessment of Allergy Testing Methods in Horses." Journal of Equine Veterinary Science, 34(6): 767-774.

These research findings reinforce that IDST provides more accurate and clinically relevant results, especially for formulating effective immunotherapy. 

Dr. Rexo scoring patient response to a set of pre-selected allergens

Final Thoughts

If your horse shows signs of allergic skin disease such as itching, hives, or recurrent dermatitis, it is crucial to get an accurate diagnosis before starting treatment. While serology testing is common and convenient, it can produce misleading results due to anti-CCD antibodies.

Request Allergy Skin Testing through a veterinary dermatologist whenever possible to ensure you identify the true allergens affecting your horse. This approach improves treatment success, reduces unnecessary expenses, and enhances your horse’s comfort and quality of life.

If you have questions about allergy testing options or want guidance on managing your horse’s allergic skin disease, contact a veterinary dermatologist experienced in equine care. Accurate diagnosis is the foundation of effective treatment.