Interpretation of Results
Results are reported as negative, borderline, positive or high positive rather than numerically since the presence and quantity of allergen specific serum IgE does not necessarily correlate with the severity of clinical signs (Lee et al 2009) and is not an indication of the significance of the allergen.
Negative results do not rule out a diagnosis of atopy or a hypersensitivity disorder but preclude the use of allergen avoidance or allergen specific immunotherapy as disease management tools.
Significant cross reactivity exists between some common allergens and has important implications in terms of diagnosis and treatment:
Alder and Hazel are closely related taxonomically to Birch; all are members of the Betulaceae family and share a major antigen, Bet v 1. Patients who are Bet v 1 sensitised are usually sensitised to pollen from all three trees. In terms of both diagnosis and treatment, Birch is sufficient to represent other members of this family.
Birch also contains the allergen Bet v 2; this is a pan-allergen (a highly conserved allergen found in almost all extracts of vegetable origin). Patients who are Bet v 2 sensitised are polysensitised to many plant species.
Cocksfoot shares major antigens with Meadow grass and Meadow fescue, Rye shares antigens with Wheat and Barley, Timothy shares antigens with Bent grass. Therefore, Cocksfoot, Rye and Timothy are sufficient to diagnose and treat patients sensitised to these other grasses (Festuceae).
Patients with positive reactions to certain pollens may have positive food results due to cross-reactivity. For example, IgE raised against pollen from Festucaea may cross react with Soya bean, Corn, Wheat and Pea. IgE raised against pollen from Betulaceae may cross react with carrot.
Treatment options – environmental testing
When faced with positive serology results, options include:
- Allergen specific immunotherapy (desensitisation)
Allergen avoidance should always be attempted. In situations where it is practical it may alleviate or, at least, significantly improve clinical signs. For example, horses allergic to Culicoides spp. should be stabled at dawn/dusk when midges are most active and fly screens should be fitted over stable doors. Ceiling fans, to create a draught, should be used alongside fly repellents and anti-fly rugs.
Pocket-sized botanical illustrations are provided for owners when serology results indicate pollen sensitisation; the cards help owners to identify, therefore avoid, the relevant grasses, weeds or trees, in their own garden and when out walking.
We have produced a unique pollen calendar which indicates the average pattern of pollen release for the UK. This is issued with veterinary results for patients who are pollen sensitised, and helps to predict periods of high allergenic load (which may be associated with clinical deterioration).
When mite results indicate sensitisation we provide information cards containing practical advice regarding the source of mite allergens and strategies to reduce the level of environmental contamination.
The effect of age on test results
Serology results from patients less than 12 months old are associated with an increased risk of both false negative and false (temporarily) positive results (allervet®, unpublished data).
Although atopy may be recognised clinically in dogs less than a year old, these patients are immunologically immature; the results of serology may change if they are tested prior to, then after, 12-18 months of age when there may be evidence of/further sensitisation, or apparent desensitisation.
If a young animal is sensitised but all of the IgE is mast cell bound, IgE will not be detected in serum. In addition, animals less than 12 months old have not experienced a “full calendar year” of allergens and there is the possibility of further sensitisation with exposure to novel antigens.
Positive results in immature dogs may subsequently become negative due to improved protection at mucosal surfaces. The primary effector molecule of the mucosal immune system is secretory IgA (an IgA dimer). Serum IgA concentrations do not reach normal adult levels until 12-18 months of age; this transient IgA deficiency may manifest clinically as upper respiratory tract infection, otitis externa, Staphylococcal and atopic dermatitis (Schalm’s Veterinary Haematology).
To summarise: evidence of sensitisation in juveniles may be present, however, retesting when animals are over 12 months old is always recommended prior to embarking on immunotherapy. Atopic phenotypes who initially test negative should also be retested at a later date if immunotherapy is a potential therapeutic option.
Allergen specific immunotherapy
Immunotherapy may be more effective than allergen avoidance for animals sensitised to a wide range of environmental allergens.
The concept of immunotherapy is not new; empirically derived protocols have been practised for many years. As a direct result of wide and successful use of immunotherapy in the human field, the World Health Organisation now advocates this as the most appropriate rationale for treating human allergy.
The objective of immunotherapy is to administer increasing doses of allergen to a point where the patient’s immune system becomes “tolerant”. Moderating the immune response reduces the frequency and severity of hypersensitivity reactions.
Immunotherapy requires commitment and will not work for all patients, however, studies show a positive response to immunotherapy in 81% of pets with atopic dermatitis (Gonzalez, Yuste et al 2003), (Gonzalez et al 2004).
Immunotherapy is not a “quick-fix” for atopic disease; if successful, maintenance therapy is usually required for several years. In some cases immunotherapy may actually cure atopic disease, rather than promoting clinical remission.
Animals suffering from atopy may become sensitised to an increasing number of allergens over time and in some cases it may be necessary to repeat diagnostic procedures and review immunotherapy accordingly.