Is food really making you ill? - Allergy and Intolerance Tests
Food Allergy and Intolerance Tests
Reliable Tests
Diagnosis of food allergy can only be made with any degree of confidence by a trained clinical doctor or allergist, using a process combining holistic assessment, with a consideration of your symptoms, your medical and family history, and good – but by no means infallible – laboratory and outpatient testing procedures.
Other past or present allergic conditions, such as asthma or pollen sensitivity, must be considered. So must seasonal or environmental sensitivities or reactions, possible occupational exposure to food products, and other reactions to foods, such as intolerances. Physical tests of lung functions, and examinations of the eyes, nose and skin, can help your specialist determine what, if any, tests you should undergo.
These may be:
- Skin prick testing (SPT), where dilute drops of allergen are placed onto your forearm – the skin is then pierced through the drop with lancet, itching and a swollen red weal at the site indicate a positive reaction. Negative results have a high degree of accuracy, but positive results are less reliable, as a patient may test positive to an allergen causing no reaction in the context of everyday exposure.
- IgE blood tests, where levels of IgE blood antibodies are measured and graded according to the count. Negative results are fairly reliable (around 90%+), but positive tests have a reliability of just above 50%.
- A food challenge, which tests for the patient’s response to exposure to a suspect food. This must be undertaken at a specialist allergy centre or under medically controlled conditions, with resuscitation equipment handy in case of severe reactions.
For food intolerance, an elimination diet may be used. This is a diagnostic test diet, where suspect foods are removed for several weeks until symptoms clear, then individually and gradually reintroduced, in order to monitor reactions. The reintroduction of a food followed by accompanying symptoms is strongly indicative of intolerance. Some patients are happy to undergo ‘short and sharp’ food exclusions of two weeks, living on just a few, non-reactive foods, such as pears, rice and pork.
If symptoms clear, a food intolerance can be diagnosed and reintroduction can begin. If symptoms persist, it’s either a psychological food aversion or not food-related at all. Many intolerances are identified in this way, but other people tolerate the reintroduction of all foods without problems – a change of diet can sometimes be all that’s needed to clear up symptoms.
If symptoms do clear, culprit foods can be identified individually during the reintroduction phase. When a food is reintroduced and symptoms return soon after, that is usually enough to indication an intolerance to the food.
Strong willpower is needed to adhere to the diet, but it is diagnostically effective.
Questionable Tests
There are dozens of food allergy tests on the market, with new ones regularly being released. Many claim to diagnose food reactions via such exotic techniques, as bio-vibrational frequencies, iridology, hair mineral analysis, and reflexology. All are unproven and rejected as valid by the scientific community.
And beware of advocates resorting to over-inflating the value of anecdotal success rates. These are generally attributable to guesswork and the law of averages. Most people eat too much wheat and dairy, and most tests reveal intolerances to wheat and dairy, and most genuine intolerances are to wheat and dairy, because they form the bulk of the Western diet.
Further, eliminating dairy and wheat often leads to symptomatic relief, because the patient is compelled to replace biscuits, desserts, burgers and other processed foods, with fresh vegetables, fish, fruit, nuts and wholegrains. Any improvement in health following this regime change is likely to be because of improved nutrition, and is not necessarily diagnostic of a wheat or dairy sensitivity. It certainly does not validate any unorthodox test that have indicated otherwise.
Here are the most common alternative tests:
The Vega/Electrodermal skin test
This employs a machine that detects changes in skin resistance, in response to exposure to individual foods held within an electrical circuit. The patient holds one electrode, while another is pressed into an acupressure point to complete the circuit. It is offered by alternative practitioners. There is absolutely no evidence whatsoever that such testing can diagnose any problem with food.
ALCAT / Leukocytotoxic Test
Under this regime, food extracts are incubated with a patient’s blood samples. Changes to size, shape and quantity of white cells are deemed diagnostic of a sensitivity. This is perhaps worthy of further investigation, but at present convincing evidence is lacking. No large-scale study has yet shown the test to be accurate.
IgG Test
Some researchers believe antibodies called IgG – which are ‘gentler’ than the allergy antibodies IgE – may be involved in idiopathic food intolerances. However this is disputed by many allergists. IgG blood testing- which identifies food-specific IgG levels in the blood – is available privately, but is expensive.
A randomised controlled trial on IBS sufferers, published in the medical journal Gut in 2004, found that patients following an elimination diet based on their IgG results experienced a 26% greater reduction in symptom scored than patients following ‘sham’ exclusion diets. However, this was confined to a subset of individuals with a specific health problem. Critics have pointed out that an IgG test merely reflects recent dietary habits – it tells you what you eat a lot of. Changing that, again, can only help your health and diet by exposing you to a broader range of nutrients.
