Allergy testing explained
Posted on 6 March 2017
Statistics suggest that approximately one out of every seven children is prone to some sort of non-seasonal allergy – and this figure increases if there is a family history of allergies. Adverse reactions to foods, medications, pets, dust and pollen are on the rise, which is why proper allergy testing is critical – and could be lifesaving.
‘Allergy tests are a guide as to whether or not a person has the potential to be allergic,’ says Dr Mike Levin, a Cape Town-based paediatrician and head of the Asthma and Allergy Division at University of Cape Town. ‘But they do not predict whether a reaction will be mild or severe. The results should be compared with levels that have been shown to be truly positive, and in some cases other tests might be required.’
How does allergy testing work?
Immediate reactions are determined using two methods – either by simple skin prick tests or through actual blood testing.
A skin prick test (SPT) is a basic procedure used to determine the risk of reactions to food or air allergens. Performed at a clinic, during an SPT a tiny amount of allergen is introduced into the skin. A small prick is made through a drop of an allergen solution, where the resultant amount of swelling at the insertion point indicates allergy potential.
A blood test, on the other hand, tests for the allergy antibody directly. If you have an allergy, your immune system overreacts to an allergen by producing antibodies called immunoglobulin E. These antibodies travel to cells that release chemicals, causing an allergic reaction. The ImmunoCAP blood test looks for the amount of IgE antibodies to a specific allergen.
What do the tests show?
While neither of these tests definitively indicate an allergic reaction, they do reflect sensitisation, which is a person’s potential for allergies. A definitive allergy diagnosis requires a doctor who has experience in interpreting these tests.
‘Both of these tests will indicate the presence of IgE antibodies,’ Dr Levin explains. ‘The higher the reaction, the higher the likelihood of an allergy as opposed to what we call “innocent” sensitisation. A negative test means an allergy is almost always ruled out. And while a positive result does not automatically mean someone is allergic, it indicates the potential for an allergy to exist.’
While both SPT and ImmunoCAP tests are directed towards specific allergens, Dr Levin adds that more generalised screening tests are available. ‘There are blood screening tests that look for a mix of allergens – phadiotop tests are used for inhaled allergens and food reactions are determined by the FX5 test.’
All of these procedures are used to determine the triggers for various allergic reactions. Repeat testing is encouraged for people with a history of allergies, as they can determine the safe reintroduction of previously avoided foods.
Can I test myself?
With so many medical options available nowadays, is there a place for self-diagnosis and self-testing?
‘Many of the self-help tests are inaccurate and can actually cause harm,’ warns Dr Levin. ‘There is absolutely no evidence that ALCAT, Vega testing, pulse testing or kinesiology are of any benefit in diagnosing allergy. Skin prick or blood tests should always be performed by a trained professional and in a safe environment.’