Allergy Testing for Pets: Methods, Costs, and What to Expect

Not every itchy pet needs allergy testing. Your vet will typically recommend testing when your pet has chronic, recurrent symptoms that haven't responded to standard treatments — or when identifying specific triggers would change the treatment plan.

"I recommend allergy testing when a pet has been itchy for more than three months, we've ruled out parasites and infections, and we need to know exactly what's driving the reaction — either to start immunotherapy or to guide avoidance strategies." — Dr. Sarah Chen, DVM

Good candidates for allergy testing include pets with:

• Year-round itching that worsens seasonally — suggests environmental allergies
• Recurrent ear infections (3+ per year) with no other cause identified
• Chronic skin infections that clear with antibiotics but return within weeks
• Poor response to symptomatic treatment — antihistamines, medicated shampoos, or short steroid courses provide only temporary relief
• Owners interested in immunotherapy — allergy testing is required to formulate allergy shots or drops

Testing is generally not recommended for pets under one year old, as their immune system is still maturing and results may not be reliable. Most veterinary dermatologists prefer to test dogs and cats aged 1–3 years or older with an established pattern of allergic disease.

There are three main approaches to allergy testing in veterinary medicine. Each has strengths and limitations:

1. Intradermal Skin Testing (IDST)

Considered the gold standard for environmental allergy testing. A veterinary dermatologist shaves a patch of skin (usually the side of the chest) and injects tiny amounts of 40–60 common allergens just under the skin. Positive reactions appear as small wheals (raised bumps) within 15–20 minutes.

• Pros: Most accurate for environmental allergens, directly tests skin reactivity, performed by specialists
• Cons: Requires sedation, specialist referral, pet must stop antihistamines/steroids 2–4 weeks before, more expensive
• Cost: Typically £300–£600 / $400–$800 including consultation

2. Serum (Blood) Allergy Testing

A blood sample is sent to a laboratory that measures allergen-specific IgE antibodies. Any vet can draw the blood — no specialist visit required.

• Pros: Convenient, no sedation needed, no medication withdrawal required, can test for a wide panel
• Cons: Higher rate of false positives, measures circulating antibodies rather than actual skin reactivity
• Cost: Typically £200–£400 / $250–$500

3. Elimination Diet Trial

The only reliable method for diagnosing food allergies. Your pet eats a novel protein or hydrolysed diet for 8–12 weeks, then individual ingredients are reintroduced to identify triggers.

• Pros: Definitive for food allergies, no lab costs, can be done with any vet's guidance
• Cons: Time-consuming (8–12 weeks minimum), requires strict compliance, challenging in multi-pet households
• Cost: Prescription diet costs (£50–£100/month) plus vet consultations

Allergy test results can be confusing. Here's what the numbers and categories actually mean:

Intradermal Test Results

Reactions are graded on a 0–4 scale at 15 and 30 minutes after injection:

• 0 — No reaction (same as negative control)
• 1 — Slight swelling, barely visible
• 2 — Moderate wheal, clearly larger than negative control
• 3 — Large wheal approaching positive control size
• 4 — Matches or exceeds positive control

Reactions graded 2+ are generally considered positive and may be included in an immunotherapy formulation.

Blood Test Results

Results typically show IgE levels categorised as negative, borderline, low positive, moderate positive, or high positive for each allergen. However, it's crucial to understand that:

• A positive blood test does not guarantee clinical allergy — some pets have elevated IgE without symptoms
• Results must be interpreted alongside clinical signs — a high dust mite IgE in a pet that itches year-round is meaningful; in a non-itchy pet, it may be irrelevant
• False positives are common — particularly for food allergens in blood tests, which is why elimination diets remain the gold standard for food allergy diagnosis

Common Allergen Panels

Most panels test for groups including:

• Grasses — Bermuda, Timothy, rye, fescue
• Trees — oak, birch, cedar, pine
• Weeds — ragweed, plantain, dock
• Moulds — Aspergillus, Alternaria, Cladosporium
• House dust mites — Dermatophagoides farinae, D. pteronyssinus
• Insects — flea, mosquito, cockroach
• Dander — cat dander (in dog panels), human dander

Allergy testing's greatest value lies in enabling allergen-specific immunotherapy (ASIT) — the only treatment that addresses the underlying immune dysfunction rather than just suppressing symptoms.

How Immunotherapy Works

Based on your pet's test results, a custom serum is formulated containing small, gradually increasing doses of the identified allergens. The goal is to retrain the immune system to tolerate these substances rather than overreact.

Subcutaneous Immunotherapy (SCIT) — Allergy Injections

• Injections given under the skin, initially every few days, tapering to every 2–4 weeks
• Most owners learn to give injections at home after vet training
• Takes 6–12 months to see significant improvement
• Success rate: approximately 60–75% of pets show meaningful improvement
• Cost: £30–£60 / $40–$80 per vial (lasts 1–3 months)

Sublingual Immunotherapy (SLIT) — Allergy Drops

• Liquid drops administered under the tongue daily
• Easier for owners who aren't comfortable with injections
• Some studies suggest comparable efficacy to SCIT
• Growing in popularity, especially for cats
• Cost: similar to SCIT

Immunotherapy requires patience. Most dermatologists recommend committing to at least 12 months before evaluating whether it's working. During the initial months, your pet will likely still need symptom management with medications like Apoquel, Cytopoint, or medicated baths.

For a broader overview of allergy management approaches, see our comprehensive pet allergies guide.

Proper preparation ensures accurate results. Here's what to discuss with your vet before the appointment:

Medication Withdrawal Periods

Certain medications suppress the immune response and can cause false negatives. Typical withdrawal times before intradermal testing:

• Antihistamines — stop 7–14 days before
• Oral steroids — stop 3–4 weeks before
• Injectable steroids — stop 6–8 weeks before
• Apoquel (oclacitinib) — stop 7–14 days before
• Cytopoint injection — wait until the next dose is due (4–8 weeks)
• Cyclosporine (Atopica) — stop 2–4 weeks before

Important: Never stop medications without your vet's guidance. Your vet may prescribe alternative itch relief during the withdrawal period.

Blood tests are less affected by medications, which is one reason they're sometimes preferred — though results may still be influenced by recent steroid use.

What to Bring to the Appointment

• A list of all current medications and supplements
• Photos of skin lesions at their worst (symptoms may be mild on test day)
• A timeline of symptom flare-ups — seasonal patterns are especially useful
• Previous treatment records showing what has and hasn't worked

After the Test

Results from intradermal testing are available immediately. Blood test results typically take 1–3 weeks. Your dermatologist will review the results with you and discuss whether immunotherapy, avoidance strategies, or a combination approach is the best path forward for your pet.