RAST Testing In Dogs: A Comprehensive Guide For Owners
Understanding RAST blood tests for identifying dog allergies and atopy triggers.
RAST Testing in Dogs: A Comprehensive Guide to Allergy Diagnosis
If your dog suffers from persistent skin problems, excessive scratching, or chronic ear infections, allergies may be the underlying culprit. Identifying what your dog is allergic to is crucial for developing an effective treatment plan. One of the most accessible diagnostic tools available to veterinarians is the RAST test, or radioallergosorbent test. This blood-based allergy test offers pet owners a convenient way to identify environmental allergens affecting their dogs without the need for sedation or extensive preparation.
What is RAST Testing?
A RAST test, or radioallergosorbent test, is a blood test that measures antibodies against specific allergens to determine whether a dog is allergic to certain environmental substances. This diagnostic tool is commonly performed as part of the comprehensive workup for atopy, which refers to the skin manifestation of inhalant allergies in dogs. When your dog inhales allergens such as pollen, mold spores, or dust mites, their immune system may overreact, leading to inflammation and the characteristic symptoms of atopic dermatitis.
Allergy testing through RAST allows you and your veterinarian to identify which specific allergens may be triggering your dog’s atopy, enabling you to formulate an informed plan to address these allergies. The test works by detecting elevated levels of IgE antibodies in the blood—these antibodies are produced by the immune system when it encounters allergens.
Understanding Atopic Dermatitis in Dogs
Before pursuing RAST testing, it is essential to understand how veterinarians diagnose atopic dermatitis. The diagnostic process involves several important steps to ensure that the skin condition is indeed allergy-related and not caused by other treatable conditions.
Initial Diagnostic Steps
The first step in working with a dog with suspected allergic skin disease is to rule out non-allergic skin conditions. Your veterinarian will typically perform a skin scrape to rule out mange (skin mites), a fungal culture to rule out ringworm, and other tests based on your dog’s clinical signs and history. These preliminary tests are critical because they help distinguish allergic conditions from parasitic or fungal infections that require different treatment approaches. If these tests are negative and your dog’s clinical signs and history are consistent with allergies, your veterinarian will diagnose your dog with allergic dermatitis.
Additionally, skin cytology may be recommended to assess for bacterial or yeast secondary infections, which commonly occur when dogs scratch excessively due to allergic itching. These secondary infections can complicate the clinical picture and may need to be addressed as part of the overall treatment strategy.
Ruling Out Food and Flea Allergies
Once your dog has been diagnosed with allergic dermatitis, further testing is needed to determine the underlying cause. Atopy is technically a diagnosis of exclusion, meaning that your veterinarian must first definitively rule out food allergy and flea allergy—the two most common causes of allergic skin disease in dogs.
To rule out flea allergy, improved flea control measures may be implemented for an extended period. Even if you believe your dog has no fleas, flea allergy can develop in dogs that are exquisitely sensitive to flea saliva from even a single flea bite. For food allergy, an elimination diet trial lasting six to eight weeks must be conducted. During this trial, your dog eats a limited ingredient diet or a prescription hydrolyzed protein diet to identify whether specific food ingredients are causing the allergic response.
How is Allergy Testing Performed in Dogs?
Once food allergies and flea allergies have been ruled out and atopy has been confirmed, veterinarians have two primary techniques available for identifying the specific environmental allergens affecting your dog: intradermal allergy testing (IDAT) and RAST testing. Each method has distinct advantages and disadvantages that pet owners should understand before making a decision.
Intradermal Allergy Testing (IDAT)
Intradermal skin testing has long been regarded as the gold standard in determining the cause of atopic dermatitis. However, this test has several practical limitations. IDAT is only performed by veterinary dermatologists, which means dog owners seeking this testing must travel to a specialist—a requirement that may not be feasible for all pet owners, particularly those in areas without available dermatologists or those facing financial constraints.
Additionally, intradermal skin testing requires your dog to be sedated, and large areas of your dog’s coat must be shaved to allow the injection sites to be monitored for reactions. The procedure involves injecting small amounts of various allergens into the skin and observing each injection site for redness and swelling (called a wheal or hive).
RAST Testing: A More Accessible Alternative
In contrast to intradermal testing, RAST testing requires only a single blood sample. This blood sample can be drawn by your regular veterinarian during a routine wellness visit, making the process far more convenient and accessible. The blood sample is then submitted to a reference laboratory for analysis. Remarkably, no sedation or anesthesia is needed, and your dog will not need to have hair shaved for this test. This makes RAST testing an attractive option for dogs with severe anxiety, those in poor health, or pet owners seeking a simpler diagnostic approach.
Comparing Testing Methods
| Feature | RAST Testing | Intradermal Testing (IDAT) |
|---|---|---|
| Sample Type | Blood sample | Skin injection |
| Sedation Required | No | Yes |
| Hair Shaving | Not needed | Large area required |
| Performed By | Regular veterinarian | Veterinary dermatologist |
| Can Be Done During Medication | Usually yes | Usually requires medication withdrawal |
| Considered Gold Standard | No | Yes |
| False Positive Rate | Higher | Lower |
RAST Testing and Allergy Medications
One significant advantage of RAST testing is that, in many cases, it can be performed while dogs are receiving their regular allergy medications. This contrasts sharply with intradermal testing, which typically requires that dogs be off medication for a prolonged period of time before testing—a requirement that may not be possible if your dog is severely affected. For dogs experiencing significant discomfort from allergies, the ability to maintain their current medication regimen during testing is a substantial benefit.
Drawbacks of RAST Testing
While RAST testing offers considerable convenience, it is important to understand its limitations. Historically, RAST testing has been associated with a higher rate of false positive test results—positive results that cannot be confirmed with intradermal skin testing. False positives can lead to unnecessary restrictions on your dog’s environment and potentially ineffective treatment strategies.
However, in a practical sense, evidence suggests that most dogs treated with hyposensitization based on RAST results still experience a significant improvement in their skin disease. Approximately 60–80% of dogs experience improvement with hyposensitization therapy, although it may take some time to see benefits and some dogs require lifelong therapy.
Important Considerations About RAST Testing
While multiple companies may offer RAST testing, not all are equally reliable. Your veterinarian may consult with a local dermatologist, if possible, to determine which testing company they recommend for the most accurate results.
Some RAST testing panels also include testing for food allergens; however, the results are controversial and do not replace an elimination diet trial. If you are concerned about food allergies, an elimination diet remains the gold standard diagnostic tool.
It is crucial to understand that RAST testing is typically only worthwhile if you plan to pursue hyposensitization for your dog. The test cannot be used to diagnose atopic dermatitis itself—it can only identify the underlying cause of already-diagnosed atopic dermatitis.
What Allergens Are Tested?
In most cases, the allergens identified on RAST testing represent a wide variety of environmental substances including weeds, trees, grasses, molds, dust mites, and other common inhalant allergens. Avoidance of these substances is typically not very practical for most dogs and their owners, since these allergens are pervasive in the environment. Therefore, the true benefit of RAST testing lies in guiding the formulation of hyposensitization therapy—custom-made allergy shots designed to help your dog’s immune system become less reactive to these specific allergens over time.
The Role of RAST Testing in Treatment Planning
The primary value of RAST testing is in developing personalized immunotherapy treatments for your dog. Once specific allergens have been identified, your veterinarian can formulate custom allergy shots containing gradually increasing amounts of those particular allergens. Over time, this exposure helps desensitize your dog’s immune system, potentially reducing or eliminating allergic symptoms.
It is important to recognize that allergy testing and treatment planning should be individualized to your dog’s specific situation. Some dogs may benefit more from pharmaceutical management of allergies using medications like Apoquel or Atopica, while others may be ideal candidates for immunotherapy based on RAST results.
Frequently Asked Questions About RAST Testing
Q: Can RAST testing be performed while my dog is on allergy medications?
A: Yes, in most cases RAST testing can be performed while dogs are receiving their regular allergy medications. This is one of the key advantages of RAST testing compared to intradermal testing, which typically requires medication withdrawal.
Q: What is the difference between RAST testing and intradermal allergy testing?
A: RAST testing is a blood test that can be performed by any veterinarian without sedation, while intradermal testing involves skin injections and must be performed by a dermatologist under sedation. Intradermal testing is considered the gold standard but is less accessible and convenient.
Q: Is RAST testing accurate for diagnosing dog allergies?
A: RAST testing has a higher false positive rate than intradermal testing; however, most dogs treated with hyposensitization based on RAST results still experience significant improvement in their skin disease symptoms.
Q: Can RAST testing diagnose food allergies?
A: While some RAST panels include food allergen testing, these results are controversial and do not replace an elimination diet trial, which remains the gold standard for diagnosing food allergies.
Q: When should RAST testing be performed?
A: RAST testing should only be performed after atopic dermatitis has been diagnosed and food allergies and flea allergies have been ruled out. It is most valuable if you plan to pursue hyposensitization therapy for your dog.
Q: How long does it take to see results from hyposensitization therapy?
A: It may take several months to see significant benefits from hyposensitization therapy, and some dogs require lifelong treatment. However, approximately 60–80% of dogs experience improvement with this approach.
Q: Should I consider saliva or hair allergy tests instead?
A: There is little evidence to support the validity of saliva or hair allergy tests, and they are not recommended by most veterinarians. Blood-based RAST testing and intradermal skin testing remain the most reliable diagnostic approaches.
References
- RAST Testing in Dogs — VCA Animal Hospitals. 2024. https://vcahospitals.com/know-your-pet/rast-testing-in-dogs
- Dog Allergy Tests: Everything a Pet Parent Needs To Know — PetMD. 2024. https://www.petmd.com/dog/procedure/dog-allergy-tests
- Decoding Dog Allergies: Symptoms, Testing, and Treatment — American Animal Hospital Association (AAHA). 2024. https://www.aaha.org/resources/decoding-dog-allergies-symptoms-testing-and-treatment/
- Dog Allergy Testing: Blood Tests Vs Skin Tests – Key Differences and Expert Recommendations — VetAMac. 2024. https://www.vetamac.com/dog-allergy-testing-blood-tests-vs-skin-tests-key-differences-and-expert-recommendations/
- Allergy Testing & Treatment — Nature Coast Animal Wellness. 2024. https://www.naturecoastanimalwellness.com/allergy-testing-a-treatment
Similar Articles
Read full bio of Sneha Tete
