Allergy Diagnosis and Tests
Our Allergy super speciality clinic offers comprehensive allergy management to help in the diagnosis and treatment of allergy problems
The ideal way to manage an allergy is to avoid the substances that cause the allergic symptoms. It is, therefore, very important to first identify the substances (allergens) causing the allergic reaction.
The patient’s description of their allergy and careful questioning by the doctor goes 90% of the way to a correct diagnosis. This is usually followed by a brief examination of the relevant organs such as nose, eyes, lungs, glands and skin. Allergy tests are done to confirm the suspected allergy detected from the history.
Once diagnosed, you need to understand nature, causes and the implications of the allergy which will make future allergy control much more successful. A follow-up consultation is helpful as it provides an opportunity to discuss problems associated with the allergy and to reinforce the need for treatment.
Specific Allergy related Immunoglobulin E (IgE) is the antibody found in our blood and tissues which mediates allergy. Allergy sufferers have raised levels of IgE and it can be measured in the blood by RAST tests and also with Skin Prick Tests.
What allergy confirmatory tests are available to us?
We can perform Skin Prick tests for common Inhalant and Food allergens or measure Total IgE in the blood. Over 450 individual RAST tests are available. We can measure another allergy cell, the eosinophil in the blood, in the sputum and also in nasal samples.
1) Skin Prick Testing:
This is one of the oldest allergy tests and is the cornerstone of primary allergy diagnosis. This test is still the most highly sensitive allergy test available. It tests for specific IgE antibodies to inhalants including House dust 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. The results are immediately available. It is used to either diagnose or exclude a specific IgE mediated cause for the patient’s allergic symptoms.
How are the tests performed?
We use standardized glycerinated extracts of the various allergen extracts such as House dust mite, tree, grass and weed pollen and fungal spores. There is also a negative control (for reference).
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 six-month shelf life and should be stored in a refrigerator.
2) Allergy-confirming blood tests- RAST
There is the original old Total serum IgE blood test, which has been superseded by the newer multi-allergen screening tests. The inhalant allergy screen is called a UniCAP Phadiatop, There are over 450 individual RAST (Radio Allergo Sorbent Test) available for everything from sheep dander to sesame seeds. These are now called Unicap RAST tests and measure specific IgE in the serum to different food allergens. To simplify matters, there are various screening panels.
The advantages of this new test include improved accuracy, better safety and being less invasive.