***Please note allergy testing is only available through your veterinary surgeon *****

Mechanisms involved in the production of an allergic response:

Definition: Type 1 hypersensitivity response results from the IgE response to an antigen. In the body antigen contact activates IgE production in B-cell series lymphocytes found in the blood. The IgE then binds to mast cell Fc-receptors sensitising the mast cell. Mast cells are found in the tissues. Repeated antigen contact with cell bound IgE leads to cross-linking of receptors and finally to a tight connection of IgE molecules. This tight connection initiates a biochemical cascade causing degranulation of the sensitised mast cell and release of inflammatory mediators. Clinical symptoms of a type-1 hypersensitivity reaction are seen. The particular symptoms depend on the tissue involved.

The antigen responsible for such a reaction is called an allergen.

Methods in allergy diagnosis:

Serological tests require the taking and submitting of a blood sample for testing.

Intradermal skin tests require the injection of the allergen into the skin and the measurement of the subsequent response.

The choice of a suitable diagnostic method for allergen detection is important for any successful therapy. Test systems vary regarding specificity and sensitivity(accuracy), test principle, number and preparation of allergens and considerable differences can be found between intradermal and serological tests in general and between the various serological tests themselves.
A major disadvantage of both intradermal and serological tests is the limited number of allergens that can be tested for. An allergic cause of the disease cannot be ruled out even with a negative test result because of the large number of allergens which cannot be tested. In general the intradermal skin test is regarded as the standard test with which to compare the results of serological tests. But even the results of an intradermal test can be impaired due to the lack of standards for allergen extracts and non-specific reactions to other substances contained in the allergen solution. Also certain allergic reactions are not of the type-1 response. Serological testing can often be preferred to the sedation and clipping which is required for intradermal testing.
Some serological tests use polyclonal anti-IgE antibodies and are regarded as unreliable as IgG is also determined as well as the allergy relevant IgE. Only monoclonal antibody testing can increase the necessary sensitivity and specificity required for accurate results. Consequently intradermal tests have lost their place as the ‘gold standard’ in allergy testing.

Even further improvement has been achieved with the introduction of the Fce-receptor test. The Fce receptors are used to detect the allergen-specific IgE and this avoids cross reactions with the other immunoglobulins which would reduce the sensitivity and specificity (accuracy) of the test.

Two types of test:

The monoclonal antibody test determines group antigens first. This inexpensive and reliable test will then allow the choice of the appropriate single allergen testing.
The Fce-receptor test determines 23 single allergens in one step, or can be divided into indoor and outdoor panels.

Some examples of the single allergens tested:

Indoor panel Outdoor panel
Aspergillus (mould) Timothy grass
Penicillium (mould) Cocksfoot
Cladosporium (mould) Blue grass annual
Alternaria (mould) Rye
Storage mites (Lepido sp) Sheep sorrel
Storage mites (Tyrophagus sp) Mugwort
House dust mite (D. farinae) English plantain
House dust mite (D. pteronyssinus) Nettle
Parakeet feathers Lamb’s quarter
Guinea pig epithelium Alder
Flea saliva Oak
Birch

Allergy testing can be used to aid in the diagnosis of an allergy, or to help exclude an allergic component in a disease.
In cats flea allergens are of significant importance and these are predominantly those of the flea saliva.

Hyposensitisation

If the result of an allergy test suggests there may be some benefit from hyposensitisation (immunotherapy) solutions can be prepared which are given to the animal in increasing concentrations and increasing intervals by injection. This hopefully causes the suppression of the IgE response. However careful consideration must be given to the selection of patients for this treatment - young animals, early start of treatment and lack of complicating factors, for example.

Food intolerance/allergy

Food intolerance/allergy is a far more complex field and can involve many different types of reaction. It is therefore not wise to use IgE testing to exclude the presence of a food allergy. The usual suggestion here is to feed an exclusion diet and to reintroduce one food at a time, if this is felt to be necessary. Many pet food manufacturers have included various diets in their ranges to make this relatively straight forward. - If the animal is better why risk causing a relapse?

For more information, please contact:

Mrs Jackie Casey BVetMed MRCVS

UK Regional Manager
Vet-Med-Lab
31 Ferring Lane
Ferring
Worthing
West Sussex
BN12 6QT
tel: 01903 709109
fax: 01903 247184
e-mail: Jackie-Casey@supanet.com