Allergy tests (IgE) in cats and dogs
Allergy tests measure IgE antibodies to allergens — in blood or as reactions in the skin. The key point: they do not diagnose atopic dermatitis. The diagnosis is clinical, from signs, history and excluding other skin diseases; the tests come afterwards, to find the allergens the animal reacts to, and positive results occur in animals without allergy.
What it shows
IgE is the class of antibodies behind allergic reactions. A blood test measures IgE against specific allergens circulating in serum; the intradermal skin test injects tiny amounts of allergens into the skin and reads the reactions. Both show sensitisation — that the immune system has met the allergen — not that it causes the itch.
Groups of results on the form:
- Total IgE — the overall amount of IgE, not tied to any allergen.
- Screening test (pass/fail) — a mixture of flea, house dust mite and pollen allergens; it does not identify the individual allergen and does not replace a full panel.
- Pollens of grasses, trees and weeds — vary strongly by region.
- House dust mites and storage mites — related mites; cross-reactions between them are reported.
- Moulds, epithelia/feathers/hair, insects — further environmental allergens.
- Flea saliva and Malassezia (a skin yeast).
- Five food panels — meat/poultry, fish/seafood, dairy/egg, grains, vegetables/legumes.
Higher than reference — what it may be a sign of
- Sensitisation to an allergen, which matters only if it fits the history and the season of itching. Allergen-specific blood tests often show positive reactions in dogs without allergies.
- Cross-reaction — for example, sarcoptic (scabies) mites can cross-react with house dust mites in allergy tests.
- A positive food panel does not prove food allergy: no blood test gives consistently accurate results here.
- A positive flea saliva test — tests for flea allergy have limited accuracy and are no longer recommended; the response to flea control is used as the test instead.
Lower than reference
A negative result does not rule out allergy. Between 10 and 30% of dogs with a clinically confirmed atopic dermatitis may have a negative intradermal test, and some dogs have a disease that looks identical but without measurable IgE (atopic-like dermatitis). Antihistamines and glucocorticoids can cause false negatives on the skin test, so the vet may ask to pause some itch medicines beforehand and will say for how long. A negative food panel does not mean the animal tolerates that food.
Look at together with
- The clinical picture — history, where and when the skin itches, and exclusion of other itchy skin diseases. This, not a lab test, is how atopic dermatitis is diagnosed.
- Skin scrapings and ear swabs for mites and flea checks — parasites are ruled out first.
- An elimination diet with a challenge — the reference method for food allergy; the vet sets it up.
- Eosinophils — white cells that can rise with allergy and parasites.
Units and conversion
Total IgE is reported in IU/mL or kU/L — the same value in two notations, 1 IU/mL = 1 kU/L. Allergen-specific results are reported in EAU, the laboratory’s own arbitrary units: results from different laboratories agree poorly, so EAU from two labs cannot be compared. The screening test and the intradermal test are qualitative — the form shows positive or negative for each allergen or for the mixture. In the app each row keeps the unit printed on the form.
Reference range
The reference range is on your lab’s form — for allergy panels it is the lab’s own cut-off for “positive”. A value above it means sensitisation to that allergen, not a diagnosis. The tests are not standardised between methods or labs, and blood and skin tests agree poorly. That is why the international committee on allergic diseases of animals (ICADA) advises using them only after a clinical diagnosis, to choose allergens for allergen-specific immunotherapy or to avoid them, and not as screening.
Cats and dogs
In cats the condition is called feline atopic skin syndrome; it is diagnosed once other causes have been ruled out. Allergy testing is used much as in dogs, to find the allergens the animal reacts to, but alone it reflects exposure rather than disease. Intradermal reactions in cats are less pronounced and harder to read. Very sensitive cats may groom away almost all fleas, so few are found.
In dogs atopic dermatitis is diagnosed from signalment, signs, history and exclusion of other itchy skin diseases; a set of clinical criteria (Favrot’s criteria) helps, but it does not apply to food-induced atopic dermatitis. Allergy tests then help to find the allergens the animal reacts to. Pollen results depend on the region where the dog lives.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Hensel P, Santoro D, Favrot C, Hill P, Griffin C. Canine atopic dermatitis: detailed guidelines for diagnosis and allergen identification (International Committee on Allergic Diseases of Animals). BMC Veterinary Research, 2015; 11:196.
- Hoff S. Atopic Dermatitis in Dogs. Merck Veterinary Manual, professional version, full review May 2026.
- Hoff S. Feline Atopic Skin Syndrome. Merck Veterinary Manual, professional version, full review May 2026.
- Pucheu-Haston CM. Cutaneous Food Allergy in Animals. Merck Veterinary Manual, professional version, full review August 2025.
- Gentry C. Flea Allergy Dermatitis in Dogs and Cats. Merck Veterinary Manual, professional version, last updated May 2026.
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.