Allergy is an exaggerated immune response (Hypersensitivity reaction) to substances which are normally tolerated. Allergies are classified into IgE mediated and non-IgE mediated allergies. Immunoglobulin E (IgE) is a distinct class of serum antibody and in IgE mediated allergies the immune system produces exaggerated amounts of IgE antibodies against specific allergens.
Specific IgE (previously known as a RAST): For IgE-mediated allergy a detailed history should be taken to guide the clinician as to which allergen tests to request. Blood tests are available that measure levels of IgE against specific allergens such as inhalants, foods, medications, venoms and latex. These tests can help clinicians to confirm a diagnosis of an allergic disorder on patients with a clinical history consistent with an immediate allergic reaction. They are particularly useful when skin testing cannot or should not be performed and measurement may also be performed to monitor immunotherapy (desensitization).
Requests for multiple allergens and “rare” allergens are discouraged, as the tests are expensive and the results can be very difficult to interpret.
False positive specific IgE results can occur in patients with very high total IgE levels (such as eczema patients with IgE >5000KUA/L). Therefore positive specific IgE results in such patients should be interpreted with caution.
In patients with a convincing clinical history for food allergies, circulating allergen-specific IgE antibodies may remain undetectable because these antibodies may be directed toward allergens that are revealed following processing (cooking or digestion)
Component resolved IgE testing: This is a specialised test offered to allergy consultants. This test detects IgE to specific components of an allergen, determines which specific component triggers the positive test result and whether it may be more likely to lead to a severe rather than mild allergy.
Clinical Indications Clinical history suggestive of type I hypersensitivity sensitisation.
Reference Range Negative 0 - 0.34 kUA/L
Sample Required Rust/Yellow top
Samples should be transported at room temperature to the laboratory within 2-3 days from collection
Sample Volume Minimum 5ml.
Please note additional tubes are required if more than 10 allergens are requested.
For component resolved diagnostics testing 1 mL per allergen is required.
Notes Sheffield Protein Reference Unit or Biomnis if the specific IgE requests is not in our repertoire.