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If you suffer from allergies, allergy testing can help identify what these are, so you can effectively eliminate them and manage your symptoms. Book online today
A skin prick test is usually the first test to be done when trying to identify allergens for a particular patient. It’s quick, painless and is safe overall, and the results can be read after about twenty minutes. A tiny drop of allergen extract that has prepared in an allergen laboratory is placed on the skin and very lightly punctured by a shallow (half millimeter) lancet. If IgE antibodies are present, an itchy wheal with a diameter between 5 and 15 mm will form, rather like a mosquito bite. These wheals will then disappear in 30 to 60 minutes. There is a very small chance that a patient may develop a stronger reaction but they are carefully monitored and treatment will be given should this be the case.
The blood test that identifies if the blood serum contains specific IgE antibodies is called a specific IgE blood test (formally known as RAST). There are two kinds of test. The first (traditional test) uses an extract of the whole substance (e.g. peanut) whilst the second (component resolved test) uses extracts of the individual allergens (e.g. the component allergens of peanut Ara h1, Ara h2, Ara h8 etc.). The second type of test is better able to distinguish true from false positives and predicts if different allergies may co-exist because they cross-react.
A patch test is used to see if a skin reaction, for example eczema, is caused by contact with a specific chemical or substance. Small amounts of the various allergens being tested are suspended in petroleum jelly in tiny aluminium wells contained in strips of tape that are applied to the skin of the back for 48 hours. If this kind of test is needed, allergy specialists will usually refer the patient to a dermatologist colleague who specialises in this form of testing.
When there are conflicts between the medical history and the results of allergy tests a provocation test may be needed. The suspect allergen is then given to the patient under carefully monitored conditions. According to the allergen and the symptoms it is suspected to cause, the allergen might, in tiny but increasing doses, be breathed in, be placed in the mouth or on the lower lip, be sniffed into the nose or be applied to the conjunctiva. Although rarely needed, examples of the situations in which this type of testing might be needed would be firstly to see if a child has outgrown a peanut allergy or secondly to see if a particular antibiotic can safely be used when other tests have been ambiguous.