Serum
Minimum sample volume: 3ml
Specific IgE is produced in susceptible individuals following exposure to an allergen. The IgE is then bound to mast cells and on repeat exposure to the allergen triggers mast cell degranulation and the clinical features of type 1 hyper sensitivity (allergic rhinitis, urticaria/angioedema, anaphylaxis).
Testing for IgE antibodies to specific allergens should only be performed to confirm a clinically suspected diagnosis of allergy, and should never be used as a “screen” for allergy. The request must specify which allergens are to be tested, where there is doubt please discuss with the laboratory or with an immunologist.
Specific IgE testing to drugs is not recommended in primary care. Testing to foods should be requested only if the patient has had onset of symptoms within 1-2 hours of exposure to the food, and not if they have subsequently tolerated the allergen. There is some role for measurement of aeroallergens when the allergen can be avoided (eg cat, dog), but pollen-specific IgE need only be measured if the patient is under the care of the clinical immunology service and desensitisation is being considered.
Interpretation of results requires clinical assessment, the presence of specific IgE indicates sensitization but does not give information regarding the severity of reactions. A normal specific IgE level to an allergen does not exclude allergy to that substance, and a positive result is not diagnostic. The relevance of the level is dependent on the allergen in question.
• In food allergy, circulating IgE antibodies may remain undetectable despite a convincing clinical history. The antibodies may be directed towards allergens that are revealed or altered during industrial processing, cooking or digestion and therefore do not exist in the original food for which the patient is tested.
• Results below limit of quantitation obtained for a drug- or venom specific IgE determination indicates the absence of specific IgE antibodies to that drug or venom. Such results do not preclude existence of current or future clinical hypersensitivity to drugs or venoms.
• Samples with results below limit of quantitation obtained with ImmunoCAP Allergen Components are recommended to be tested with the corresponding extract-based ImmunoCAP Allergen, if not already performed. Such complementary extract-based testing will cover additional allergen components present in the allergen source material to which the patient may be sensitized.
• A result below limit of quantitation obtained with an extract-based ImmunoCAP Allergen does not exclude the possibility of obtaining measurable concentrations of specific IgE when testing with ImmunoCAP Allergen Components from the same allergen source. This is due to the fact that some components may be present in very low amounts in the natural extract.
• If the total IgE is very high (>1000kU/l) allergy testing becomes inaccurate due to non-specific binding.
The turn around time of these tests is variable. Please contact the immunology department to discuss these cases.
In House / Referred (dependant upon specific request)
Clinical advice is available from the Immunology Medical Team at Derriford Hospital
T: 01752 431675
Specimen Labelling Procedure
8210
