This section deals with clinical conditions associated with allergy and hypersensitivity which are covered by the Immunology department. For each clinical condition, the relevant immunological tests are listed together with a short explanation of their use.
Allergy tests may help identify which allergens suggested by the history could cause symptoms. However, the finding of allergy specific IgE in the serum does not mean that the allergen is responsible for the symptoms under investigation, nor does it necessarily indicate that avoidance measures will help the patient.
Specific IgE provides similar, although not identical, information to skin testing but is particularly valuable in assessing some groups of patients (young children, eczema/dermographism, taking antihistamines, past history of anaphylaxis), is needed to interpret the significance of the specific IgE.
Requests for “RAST” are not acceptable.
Requests should be for specific allergens as indicated by the history.
Patient information is available at:
Relevant immunological test: Allergen specific IgE (limited association)
When the allergic reaction is strictly limited to the conjunctiva allergy tests are frequently negative. When conjunctivitis is part of a more generalised allergy, specific IgE and skin prick tests are usually positive for the causative allergen.
Allergy tests may help distinguish allergic from vasomotor or other causes of rhinitis. Total IgE is often in the normal range or slightly elevated. Specific IgE may be sought to inhalant allergens.
While the range of allergens tested should be sensibly guided by a careful history this should generally include allergens to which most people are exposed, such as cat and house dust mite (HDM).
Investigation of seasonal rhinitis is only indicated if there is some doubt about the diagnosis or if desensitisation is being considered.
The pollens involved in seasonal rhinitis or asthma are as follows: grasses (May-September), trees (March-May) and weeds (July-September). There is little point in finding the exact pollen allergen unless it is intended to give the patient immunotherapy – when skin testing is mandatory.
Total IgE is usually raised in extrinsic asthma; specific IgE to relevant allergens is also detectable.
Specific IgE should invariably be sought against the house dust mite. Often this will suggest the appropriate animals (cats, dogs, horses, etc).
IgE to Aspergillus is associated with the need for closer monitoring and maybe more intensive steroid treatment. For seasonal asthma see seasonal rhinitis.
Total IgE is often markedly elevated in widespread disease and Specific IgE may be present at high level to allergens that cause no overt symptoms. Any positive Specific IgE results therefore need careful interpretation.
Specific IgE to house dust mite is often high and house dust mite allergy may exacerbate eczema in such patients.
Please refer all patients experiencing anaphylaxis to the allergy clinic for assessment. Blood samples for mast cell tryptase taken within 1-2 hours of reaction can help indicate if the reaction was anaphylactic.
Anaphylaxis and anaphylactoid reactions to anaesthetics, etc
Patients will be invited to attend the special clinic run jointly by Immunology and the Department of Anaesthesia at which they will be assessed.
Total IgE and specific IgE may help identify the causal antigen involved in type I hypersensitivity.
Relevant immunological tests
- Allergen specific IgE (to Aspergillus)
- Aspergillus fumigatus precipitins
- ANCA (See vasculitic section)
Total IgE, specific IgE to Aspergillus, and Aspergillus precipitins (IgG) should identify cases due to hypersensitivity to the fungus.
Total IgE may be raised in association with parasitic infestation.
A positive ANCA may point to a vasculitic cause (Churg-Strauss).
Evidence of specific IgE antibodies may be consistent with a diagnosis of food allergy but, unfortunately, the presence of such antibodies does not prove clinical sensitivity.
Elimination and food challenge testing may help confirm or rule out food intolerances.
Laboratory immunology tests cannot help investigate non-allergic food intolerance.
Measurement of total IgE will permit the ratio of specific to total IgE to be assessed in positive samples.
(Last reviewed June 2019)