Small Animal Dermatology, 3rd edition

178 DISEASES/DISORDERS

 Allergy testing:
Neither serum nor intradermal allergy testing can discriminate between normal

and allergic patients, or to make the diagnosis of AD

Both normal and patients with AD may have positive or negative tests

Serum and intradermal allergy test results rarely correlate

Allergy testing is necessary only for the identification of allergens to be included

in allergen-specific immunotherapy

Studies lack documentation of the accuracy of alternative forms of “allergy test-

ing:” these modalities are not recommended.

Serologic Allergy Tests

 Measure the amount of allergen-specific IgE antibody in the patient’s serum.

 Appropriate for the selection of allergens for immunotherapy when referral for intra-

dermal testing not possible.

 Negative/not relevant test results obtained from patients with atopic-like dermatitis

(non-IgE mediated) and cutaneous adverse reaction to food.

 Advantages over IDST: availability; shaving of the hair coat not needed; sedation not

necessary; no potential for anaphylactic reaction to testing material; less sensitive to

medication administration (withdrawal recommendations vary by laboratory).

 Disadvantages: frequent false-positive reactions; limited number of allergens tested;

inconsistent assay validation and quality control (may vary by laboratory).

 Reliability and reproducibility vary with each laboratory/test utilized; widely varying

results obtained from the same patient serum sent to multiple laboratories.

 Serum testing alone often performed in cats with allergic asthma to avoid sedation.

 Often submitted in conjunction with intradermal skin test results for allergen selec-

tion (best use).

Intradermal Skin Testing (IDST)

 Small amounts of test allergens injected intradermally; wheal formation is measured.

 More accurate (and physiologically relevant) method of identifying offending aller-

gens for possible avoidance or inclusion in allergen-specific immunotherapy.

 Results more variable and difficult to interpret in cats.

 False-negative test results may be caused by medications (glucocorticoids, antihis-

tamines, specific tranquilizers), diluted/weakened allergens, and/or severe stresses

(physiological or medical).

 False-positive test results may be caused by irritant or contaminated allergens and/or

poor testing technique.

 Testing not affected by cyclosporine, oclacitinib, or neutralizing IL-31 antibody.

Skin Biopsy

 Skin biopsy is most useful in AD to reinforce the diagnosis and to exclude other likely

causes of pruritus.