Simply put, an allergy occurs when your body’s immune system develops an acute hypersensitivity to harmless substances in your environment.
Allergic reactions can be triggered by house dust mites in your bedding, grass pollens in the summer breeze or peanuts taken in the diet. In-day-to day life, these substances would usually pose no threat, but if the body “mistakenly” feels under attack and responds with a severe hypersensitivity, then this can result in a life-threatening reaction as the body releases destructive chemicals causing swelling, itching, rashes, low blood pressure, throat closure and breathing difficulties. Some families are called “Atopic” as they have a genetic predisposition to develop allergies such as food allergies, eczema, asthma and hay fever.
Why test for allergies?
Many conditions including asthma, hay fever, sinusitis, eczema, hives, stomach aches can be caused by one allergy or another. If we can identify the allergic cause then the treatment will be easier and ranges from simple avoidance, to desensitisation and symptom control via specific medication. For example if a new kitten is causing your asthma to deteriorate, then it makes sense to find a new home for the cat rather than take medication every day of your life; and if grass pollen is the problem, then being desensitised to grass pollen may induce a state of tolerance and reduce or eradicate the need for antihistamine tablets, eye drops and nose sprays.
Skin Prick Testing
Skin Prick testing is the oldest and most reliable form of allergy testing. Extracts of inhalant and food allergens are applied to the skin in droplet-form and the skin is then superficially “pricked” using a special blunt lancet. This allows some of the droplet to penetrate the outer layer of skin and set up an allergic response if allergic to the allergen. The response results in an itchy bump the size of your little finger nail if allergic and nothing at all will happen if not allergic.
We test for various inhalant allergens such as house dust mites, pet dander, pollen from trees, grasses and flowers, mould spores and feathers. The commonest food allergens include dairy, egg, wheat, gluten, soy, nuts, seafood and yeast and all of these are included in our testing. Any number of allergens can be tested and fresh fruits, nuts, vegetables and exotic foods can be used to create a testing extract. So if you have a specific product or food you suspect, bring along a raw sample and we can make an extract. After the test, the itchy bumps will disappear within 45 minutes. Children can accurately be tested from the age of 4 months. All antihistamine medication must be stopped for 2 days prior to skin prick testing.
Intradermal Tests are a form of skin prick testing, where a trace of the allergen is injected into the skin to raise a small bleb. If allergic, the bleb will itch and turn red. This test is mainly used in local anaesthetic and antibiotics allergy testing, when the skin prick test is negative but an allergy is suspected.
RAST blood testing
If there isn’t a skin prick test available, or the person has bad eczema and the skin cannot be tested, then we recommend a RAST (Radio-Allergo-Sorbent Test) on a blood sample. This test detects specific IgE antibodies produced by the body’s immune system. The problem with this test is that you get a lot of false positive results (the test shows a low grade of reactivity, but you are able to eat that food or be exposed to pollen without reacting). The modern CAP technology is now used and local Pathology laboratories process these tests, such a Lancet, Pathcare and Ampath in South Africa, All these tests are covered by Medical Aid Insurance and over 400 individual CAP RAST tests are now available.
Measuring Total IgE – a word of caution: We historically made use of Total IgE as an indicator of probable allergy. Although this test is positive in many allergy sufferers, some people with no allergies can have non-specifically raised Total IgE. For example in non-allergic eczema we can see very high levels of Total IGE, whereas in allergic rhinitis, the Total IgE may be paradoxically low while a specific IgE test for pollen is more accurate.