Allergy Testing – Is it necessary?
Yes, allergy testing is the only way to detect the specific cause – be it food, environment, drugs etc. Most food allergies are due to regular nutrition items in the diet and accurate identification prevents their unnecessary removal.
The environmental allergens are invisible and can only be recognised by testing. Aero-allergen control is advised and proper management of allergic foods. In treatment resistant cases, allergen control improves the response to conventional drugs.
Is one test enough?
For eczema and digestive problems in children under the age of 3 years, food testing is relevant.
Thereafter. testing for both, food and airborne allergens are relevant for all patients.
Types of Tests
1. Skin Prick Test
The doctor will assess the skin on the inner forearm of the patient, and will usually choose this site for testing on. Occasionally, the back is used. The skin is cleaned and then little drops of specialized allergen extracts are put on the skin and each is marked with a pen. A small prick/scratch on the skin is done through the drop which does not cause any bleeding and is very well tolerated, even by infants. The drops are then wiped off and the reaction in the skin is read by the doctor after 15minutes. The responses resemble mosquito bites and can be itchy.
Is it safe?
The allergist performs the skin testing in a centre which has all the facilities and training to handle serious reactions, though these occur extremely rarely. Serious immediate allergic reactions to airborne allergens are extremely uncommon. Very rare, serious outcomes may include an early allergic reaction to the testing in the form of asthma or breathing difficulty. This will be treated immediately by the doctor.
How do I prepare for my allergy test?
It is essential that all anti-allergy medications (antihistamines) are stopped for 5 days before the test as they interfere with the body reaction and the test would be considered invalid.
If uncertain about any medication that you are on, please do not hesitate to call and ask ahead of time with your list of medications and you will be advised accordingly.
Some medications can affect skin testing results. Please inform the doctor performing the test whether you are taking cold and flu tablets, antacids, antidepressants or beta‐blocker medications.
Is the skin prick test a confirmatory test?
For dietary allergens, in order to confirm the offending allergens, after the skin prick test is performed a special diet called an oral food challenge (OFC) is done. For a short time the suspected foods are removed from the diet and thereafter reintroduced in a specific way as prescribed by the allergist.
For environmental allergens, the test provides sufficient information for the allergist to go ahead and advise about environmental control measures.
2. Patch test
Patch testing is a method to diagnose the cause of skin reactions that occur after substances repeatedly touch and cause allergic reactions in the skin such as jewellery and cosmetics.
- • Possible allergens are taped to the skin for 48 hours.
- • The allergist will look at the area in 72 – 96 hours.
3. Intra-dermal Testing
This is a slightly more invasive but sensitive test than the skin prick test recommended for use in certain situations. 0.05 — 0.1ml of the allergen extract is injected into the very outermost layer of the skin of the arm. The result can be read at 20-30 minutes and in some cases at 24 hours and at 48 hours. It is generally avoided in children.
4. Allergy Blood Test
The commercial blood tests routinely available currently are of limited value and costly because they are predominantly focused on allergens found in temperate climates and western diets. However, specially tailored panels of blood tests are available at The Allergy Clinic relevant to the tropical aeroallergens, and can be requested and interpreted by the allergist for specific patients. For food allergies, blood tests are not routinely recommended; however under special circumstances directed by the allergist, they may be requested and again, would be diet/culture appropriate.
Examples of Environmental Allergens Tested
Examples of Food Allergens Tested