We know we’re in for a treat when ‘The Webinar Vet’ organises for three well respected dermatologists to lead a webinar discussing allergy testing in dogs. Anthony Chadwick was one of three dermatologists and he started this webinar by introducing his two counterparts, Kristian Pedersen and Albert Carre-Llopis. The format of this webinar consisted of an interactive discussion between all three dermatologists about all aspects of allergy testing.

Between all three, they delivered some key take home messages, one of which was understanding why and when we should be performing allergy testing. It was explained that an allergy is a clinical condition which can only be diagnosed by excluding other differential diagnoses such as parasitic disease and infection. It is imperative to understand an allergy cannot be diagnosed from the results of an allergy test. The results from an IgE serology test, for example, will only tell you if a patient has been exposed to a particular allergen and whether they have been IgE sensitised to that allergen. Decisions can only be made about what a patient is likely to be allergic to and what allergens need to be added to an immunotherapy vaccine when serum IgE results are combined with the patient’s full clinical picture. Anthony was also very keen to stress that allergy testing should only be performed and is only necessary when an owner is willing to commit to allergen specific immunotherapy.

IgE serology testing for food allergy was another area discussed and it was established that the only sensible option for diagnosing food allergy is to perform a food elimination trial and re-challenge. Serum IgE testing for food allergy only becomes relevant in helping to compile an appropriate diet for the food allergic patient.

Serology IgE testing is now commonly performed by the veterinary profession to determine the make-up of an allergen specific immunotherapy vaccine. However, there can be issues when attempting to interpret the results from an allergy panel. For example, false positives can sometimes occur as a result of cross reactions between certain allergens such as sarcoptes mites and house dust mites. There is also a subset of dogs which produce IgE which binds to carbohydrate (CHO) allergens. These CHO allergens are shared in common by pollens tested for within an allergy panel and the presence of anti-CHO IgE will lead to pollens testing positive despite them being completely irrelevant to a patient’s clinical disease.

There is a test which can be performed to check for CHO reactivity within serum and if found to be present the anti-CHO reaction can be blocked so it has no effect on test results. This CHO reactivity test is an important step for any lab undertaking allergy testing to perform and it is key to ensure the lab chosen to perform a practice’s allergy testing is experienced and knowledgeable in all aspects of this process.

Twenty to thirty per cent of serology tests can also test IgE negative for all allergens in a panel despite being confident that a patient is suffering from atopy.  These individuals are labelled as having ‘atopic-like disease’ and although it is not fully understood why these patients are IgE negative, it is thought it may be because they are suffering from non IgE mediated disease  or have a very low IgE response which is not picked up on testing.

This webinar ended with interactive questions from the participating audience and was initiated by a member delegate asking ‘if a dog has responded well to immunotherapy, when is it appropriate to stop immunotherapy?’ ‘After two to three years’ was the answer delivered but, Anthony advised, in his experience there are three subsets of dogs which react in different ways. In about 20-30% of cases immunotherapy appears not to be effective even after one year of treatment. At this point the therapy can either be stopped or continued on for a further year to see if there is any improvement further down the line. The second group are those which respond well to immunotherapy but when trying to extend the injection interval after two to three years of treatment, the dogs start to show clinical signs again. Obviously, in these cases, the immunotherapy should be continued long term. Finally there is the third group where immunotherapy works very well, the injection interval can be extended without any deterioration and in some cases dogs can come off immunotherapy altogether and appear effectively ‘cured’.

Sublingual immunotherapy was also discussed at question time and it is considered a very easy product to administer but it does need to be given twice daily which could potentially lead to problems with owner compliance. It is however, a more stable preparation compared to the injectable version and can be kept at room temperature.

During the course of this webinar Anthony thanked the membership for allowing him to indulge in his favourite topic, dermatology, by organising and delivering this webinar alongside two dermatologists for whom he obviously has a great deal of respect. In my opinion, this webinar was (as stated at the start of this blog) ‘a real treat’ to participate in and if Anthony wishes to organise more of the same then please do!