Intradermal and serum allergy testing is performed to identify environmental allergens.
In animals suspected to have atopic dermatitis (environmental allergies), we often recommend allergy testing to determine the components of a specially formulated immunotherapy (allergy shots or drops).
Intradermal Allergy Testing (IDAT)
Skin testing is the preferred method since we're testing the affected organ. Certain drugs, like steroids and antihistamines, need to be stopped prior to skin testing. Animals are sedated, the hair is clipped on one flank, and ~50 allergens are injected into the skin (indoor and outdoor, house dust mites and pollens in particular). Positive and negative controls are used to gauge the response. Saline is used as a negative control since it has no allergenic properties. Histamine is used as the positive control since it reliably causes an allergic reaction. Allergens are compared to the controls. A subjective scale (based on size redness, turgor) of 0-4 (dogs) or 0-2 (+/-, milder reactions in cats) is used.
Serum Allergy Testing
Subtle skin test responses are more common in cats, so we usually start with blood testing in cats and circle back to skin testing if needed (i.e. few or no positives = non-atopic individual). Other reasons for starting with or only performing a blood allergy test: high risk for sedation, extremely high anxiety despite a behavior consult and follow-up (cortisol release may mask IDAT results), or patient is on medications that cannot be stopped and would interfere with IDAT.
- Testing for the purposes of avoiding allergens is neither recommended nor successful since our pets don’t live in sterile laboratory environments.
- Environmental allergies are a diagnosis of exclusion. This means that we should have arrived at this diagnosis before pursuing testing. It is a "treatment test" and not a "diagnostic test" - we formulate treatment with the information obtained.
- The only way to diagnose food allergy is with a food trial. Skin or blood testing for food allergy is not recommended. The results from those tests do not correlate well with actual food allergy (many false positives and negatives) or with each other (extreme differences between companies mean none are accurate at this time).
- Saliva/hair testing for any allergy does not provide viable information.