Allergen-Specific
IgE Testing

Allergy assessment in routine clinical practice

All secondary immune responses result from previous exposure, including allergy, although that exposure may be difficult to identify (e.g. food allergens in infants or toddlers). The exposure history is usually centred on the clinical manifestation of allergic or possible allergic symptoms and signs. These may be obvious, particularly with food allergy where oral symptoms may arise within seconds to minutes following exposure (oral allergy syndrome, OAS), or they may require more or less detailed examination of the environment.

Some simple approaches may be useful in persons with limited allergies: pollens are prominent outdoors in spring and summer; house dust mite indoors and year-round; animal dander following specific exposures.

There are also many overlapping allergies due to the fact that allergens are often highly conserved, shared peptides in related species (e.g. certain foods, pollens, insects). This information is important in selecting laboratory testing for specific IgE, which can be used to manage severe or nuisance allergies through avoidance and/or immunotherapy.

Both skin prick testing (SPT) and serum-specific IgE are useful for identifying the presence of allergen-specific IgE in a given patient and are useful in the assessment of allergic rhinitis. However, the presence of antibody does not equal disease, and results must be interpreted in the clinical context.

Common respiratory allergens

• House dust mite
• Pollen
• Animal dander
• Mould

Food allergens 

Food allergens present several diagnostic difficulties, partly because only certain foods or components are mandated in labelling by Australian food standards, and partly because of unseen contamination (e.g. during food preparation). Furthermore, some non-food items (e.g. cosmetics) may contain food allergens. Food ingestion may result in a variety of clinical manifestations, ranging from OAS and skin reactions to life-threatening anaphylaxis. Most food allergens are primarily managed by avoidance, but diets can be restrictive, so it is important to correctly identify the relevant allergen.

According to current information, ASCIA states that food allergy occurs in around 2-4% of Australian and NZ adults, with increased numbers in childhood (5-10%) and up to about 10% in infants. Again, SPT and specific IgE are useful for identifying the presence of allergen-specific IgE in a given patient. Elimination diets and challenge may be required but should be conducted under specialist advice and supervision.

Common food allergens

• Egg
• Cow’s milk
• Peanut
• Tree nuts (most commonly cashew, pistachio, hazelnut and walnut)
• Sesame
• Soy
• Fish
• Shellfish
• Wheat

Adverse drug reactions (ADRs)

Adverse drug reactions are probably the most complex clinical events requiring consideration of an allergic response. ADRs are classified Type A if they are predictable due to the known properties of the drug and Type B if they are unpredictable or idiosyncratic. Type B reactions include allergic reactions that may be IgE-mediated immediate responses (including anaphylaxis) or several cell-mediated immune responses.

The clinical history is crucial in assessing drug reactions of all types. While serum-specific IgE is available for the investigation of some potential drug allergies, specialist clinical assessment some be required. It is important to consider de-labelling some patients who believe they are penicillin-allergic, since potentially important therapeutic interventions may be unnecessarily curtailed.

Insect venoms

Insect venoms are an important cause of allergy, including anaphylaxis. Specific IgE is available for most clinically important insect venoms.

For further information about allergy testing at Clinical Labs, including our doctor brochure, allergen-specific IgE order form, clinical articles and current pricing, click here.

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