What allergy confirmatory tests are available to us?
Skin Prick Testing
This is one of the oldest allergy tests and is the cornerstone of primary allergy diagnosis. It was first performed by Dr Charles Blackley who was a Manchester GP and Homeopath, to identify grass pollen as the cause for Hayfever in 1865. This test is still the most highly sensitive allergy test available. It tests for specific IgE antibodies to inhalants including Housedust mite, pollen, cat and dog dander but can also be used to test for food, venom and drug allergy. A positive result is a typical raised wheal and red flare reaction on the skin. It is used to either diagnose or exclude a specific IgE mediated cause for the patient’s allergic symptoms.
The newer ALK Abello and Diagenics (Allergopharma) glycerol based extracts are highly standardised and accurate. They are cheap, safe and simple to perform if someone in your surgery has been trained to use them and the results are then immediately available. These tests are useful to demonstrate to the patient the acute inflammatory nature of allergy. They are particularly accurate in diagnosing the cause of asthma and rhinitis. Other international manufacturers of reputable skin prick test reagents include Allergy Therapeutics, Stallergens, Allergopharma and Dome Hollister.
Prick and Prick tests for food allergy are performed using a drop of the fresh food. The skin is pricked through the drop of fresh extract ( for example in diagnosing allergy to apple).
How are the tests performed?
We use standardised glycerinated extracts of the various allergen extracts such as housedust mite, cat and dog dander, tree, grass and weed pollen and fungal spores. There is also a negative saline and positive histamine control (for reference).A drop of each extract is placed on the inner aspect of the forearm about 3cm apart and we prick through the drop at 90 degrees to the skin using a specially modified lancet. Using firm controlled pressure and making sure not to draw blood.
The reactions are read after 15 to 20 minutes and a positive reaction should have at least 3mm of raised wheal. All oral antihistamines should be avoided for 2 - 3 days before hand, as they suppress skin reactivity. The kit has a read more
