Dog Allergy Testing: Blood Tests vs Skin Tests – Key Differences and Expert Recommendations

When a dog presents with a history of seasonally inflamed, itchy skin that doesn’t respond well to maintenance medication, veterinarians often suspect allergies.

After ruling out parasites, skin infections, and other common causes of pruritus and inflammation, the next logical step is typically recommending allergy testing.

Benefits and Limitations of Allergy Testing for Dogs

Allergy testing is a valuable tool for identifying the underlying causes of atopic dermatitis in dogs, which is commonly triggered by inhaled allergens like pollen, mold spores, and dust. However, it’s important to note that allergy testing is not recommended for diagnosing food allergies, which require a food trial with a hypoallergenic diet for confirmation.

Additionally, allergy testing cannot diagnose atopic dermatitis itself. Atopic dermatitis must be diagnosed first through a thorough evaluation of medical history, clinical signs, and the exclusion of other skin conditions. Allergy testing is most useful once atopy is diagnosed, helping to identify specific allergens for targeted immunotherapy or other treatments aimed at reducing allergic reactions.

There are two primary methods of allergy testing in dogs: intradermal skin testing and blood (serum) testing. Each method offers unique benefits and limitations, both medically and from a client perspective.

Intradermal Allergy Testing for Dogs: How It’s Done and What to Expect

Intradermal allergy testing involves injecting small amounts of allergens just under the skin to identify allergic triggers in dogs. This procedure is usually performed under sedation or general anesthesia, with strict monitoring to ensure the patient’s safety. Typically, 40-60 allergen injections are given in a single area of the body, such as the lateral thorax or abdomen.

A “positive” reaction appears as a visible swelling, similar to a hive, which typically forms within 20 minutes of the injection. If no swelling occurs, the dog is considered not allergic to that specific allergen.

By carefully assessing the skin reactions at each injection site, a veterinary dermatologist can identify the allergens responsible for triggering the dog’s atopic dermatitis, guiding treatment options and allergen-specific therapies.

Pros and cons

Intradermal allergy testing is widely regarded as the “gold standard” for diagnosing atopic dermatitis in dogs. Other allergy tests are often compared to intradermal testing for accuracy and reliability.

However, there are important precautions and restrictions for pets undergoing intradermal allergy testing. Female dogs should not be tested if they are pregnant or in heat, as hormonal changes can affect test results. It is also recommended to test pets at the end of their allergy season, typically in the fall, for the most accurate results. Pets should not have a bath for five days prior to testing, and they must be fasted the morning of the procedure to ensure safe sedation.

Additionally, intradermal allergy testing cannot be performed if the patient has recently received certain medications, as they may interfere with the test results.

• Long-acting injectable steroids within the last 90 days
• Oral steroids within the last 30 days
• Topical steroids (including ear or eye medications) within the last 14 days
• Antihistamines within the last 7 days
• Essential fatty acids within the last 7 days

Intradermal allergy testing can present challenges for some dogs, especially those who experience extreme pruritus (itchiness) when medications are discontinued. This can make the testing process more difficult for patients that are sensitive to the cessation of allergy treatments.

Another limitation is the need for sedation or anesthesia, which may not be suitable for dogs with certain underlying medical conditions. Additionally, some pet owners may be reluctant to pursue sedation or anesthesia due to concerns about the risks involved.

All hair at the test site must be clipped. With the right veterinary table, it’s a minor inconvenience for most pets, but could be a significant disadvantage for show dogs or dogs judged based on their appearance.

Finally, intradermal allergy testing requires an experienced veterinary dermatologist to administer the test and interpret the results. The skin reactions at each injection site can be subjective, and distinguishing between normal and allergic reactions requires specialized expertise. This can be an obstacle for pet owners in rural areas who may not have access to a veterinary dermatologist or mobile veterinary care, requiring long-distance travel for testing.

Blood Allergy Testing for Dogs: Procedure and Considerations

Blood allergy testing involves drawing a blood sample from the dog and sending it to a laboratory for analysis. The lab then tests for allergen-specific antibodies (IgE) against various allergens that may contribute to atopic dermatitis.

There are several laboratories that offer blood allergy testing, each utilizing different techniques. These methods can vary in terms of accuracy and clinical relevance. Veterinarians should carefully evaluate and choose a laboratory based on its methods, reputation, and the reliability of its results to ensure the best care for their patients.

Pros and cons

Blood allergy testing is a convenient option for diagnosing allergies in dogs. It can be performed in general practice without the need for a specialist to administer the test or interpret the results. Since it doesn’t require sedation or shaving, a simple blood sample can be collected during a routine wellness visit, making it less invasive for the patient.

However, blood allergy testing has its limitations. One common issue is the risk of false positives, where the test shows a positive result that cannot be confirmed by intradermal skin testing. Additionally, positive serum allergy test results have been observed in dogs with no clinical signs of atopic dermatitis. In some cases, the levels of allergen-specific IgE detected by blood testing may not correlate with the severity of the dog’s clinical symptoms.

The findings from blood allergy testing can sometimes raise concerns about its accuracy. When there is a discrepancy between the results of intradermal and blood allergy testing, intradermal testing is generally considered the more reliable method.

However, some reports suggest that dogs treated based on blood allergy test results still experience clinical improvement, despite the potential limitations of this test. For dogs that are not candidates for intradermal testing, blood allergy testing may still be a viable option.

One significant advantage of blood allergy testing is that it does not typically require pets to discontinue their medications before testing. This can make the process more accessible to pet owners, as many are hesitant to stop their pet’s medications for the extended withdrawal periods required for intradermal allergy testing.

Which allergy test is best for dogs?

Ultimately, there is no one “best” test for all dogs.

Intradermal allergy testing is often considered the “gold standard” and the most accurate method for diagnosing allergies in dogs, but it does come with certain limitations. For pet owners who are unable or unwilling to pursue intradermal testing—due to the need for medication withdrawal, sedation, travel to a specialist, or shaving the dog’s hair—blood allergy testing can provide a practical alternative with many of the same benefits.

While blood allergy testing may produce different results than intradermal testing, many dogs still experience significant clinical improvement when treated with immunotherapy based on the blood test results.

For some dogs, a combination of both skin testing and blood testing offers the best approach. By analyzing the results from both tests, veterinarians can make more informed immunotherapy decisions. Dermatologists may recommend this dual testing strategy for certain cases, although the cost of testing may influence whether pet owners opt for both tests.

By carefully assessing the skin reactions at each injection site, a veterinary dermatologist can identify the allergens responsible for triggering the dog’s atopic dermatitis, guiding treatment options and allergen-specific therapies.

Sources and Further Reading on Dog Allergy Testing

• Rees, C. 2011. Atopic dermatitis in cats and dogs. 
• Roosje, P. 2010. World Small Animal Veterinary Association World Conference Proceedings. Bern, Switzerland.
• University of Wisconsin Veterinary Care. 2018. Allergy Testing for Your Pet. Available at: https://uwveterinarycare.wisc.edu/wp-content/uploads/2018/04/Allergy-Testing-2018.pdf
• Canada West Veterinary Specialists. Allergy Tests for Atopic Dermatitis. Available at: https://canadawestvets.com/forms/DermatologyIntradermalAllergyTestProtocol.pdf