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The same food can cause a variety of different reactions in different people; food sensitivities do not act on the immune system in the same way as, say flu does. There are a number of tests available, via a number of sources, and all have different merits. No test is absolutely perfect, but some are more helpful in ascertaining the root cause of problems than others.
Scientific Tests, in the main, can only act as a guide to potential troublemakers. The only way to confirm that a food is the cause of the problem is by a careful, medically supervised, elimination and challenge diet. It is vitally important that other conditions are considered and rejected before food sensitivity is diagnosed: the symptoms of food allergy and intolerance, particularly in the gastrointestinal tract, can be mistaken for a variety of other problems.
Self-diagnosis is not condoned by any authority. It is too easy to cut out vital nutrients while eliminating foods, and it is possible to do much more harm than good while doing this. It is much, much, more sensible to engage the help of a professional allergist or dietician, who can give full advice on which foods to avoid, and how to replace them with suitable alternatives so that you remain healthy. This advice is particularly important when children are involved; professional help is vital to ensure that they receive all the nutrients necessary to grow properly. It can be harmful to unnecessarily restrict foods that are not involved, not only because of the potential for nutritional deficiency. In today’s society, where much of our cultural identity comes from food, cutting out foods may have a negative effect on the patient’s quality of life, and their emotional health. This may, at its worst, lead to a food phobia, or even anorexia nervosa.
The intradermal, or scratch test (and the sublingual, i.e. under the tongue, test) are the favoured tests of medical allergists. The skin is pricked, or scratched, and the suspect substance is applied. Alternatively, a small needle is used to inject a drop of fluid containing a known allergen just under the surface of the skin. This can be done on the forearm, or on the back (particularly when young children are taking the test so they don’t have to see what’s going on). It is not painful and is effective for inhaled and contact allergens, and foods. If a red weal appears within fifteen to twenty minutes, then the substance has been determined to cause an allergic reaction. This is known as the weal-and-flare response. The larger the weal, the stronger the allergy. The weal fades with in a few hours. The advantage of the scratch test is that many allergens can be tested at one sitting.
Negative skin tests for IgE reactions to highly allergenic foods such as wheat, egg, peanuts, fish, milk and tree nuts are 95% accurate. Other foods produce a 30-50% accuracy rate for negative tests. False negative tests can be due to a variety of factors.
• The reaction may not be mediated by IgE antibodies.
• The allergen extract may contain none of the specified allergen.
• The allergen may have been denatured during the preparation process.
• The skin’s mast cells may not react to the allergen, even if the gut does. It may be the case that a recent severe allergic reaction has raised the levels of IgE in the body.
However, positive reactions to skin tests are less than 50% accurate. Latent food allergies can skew the results, causing a positive reaction to the skin test (the IgE antibodies are present), while eating the food causes no symptoms. Commercial allergen extracts contain histamine themselves. Since histamine is involved in allergic reactions, so the presence of histamine itself can cause a positive reaction. The food may simply be an irritant to the skin, even if it doesn’t affect the digestive system - skin mast cells are more sensitive to a wider range of stimuli than those in the digestive tract. Around one third of patients who have positive skin prick tests show clinical symptoms during a food challenge. Skin prick tests tend to work best for inhalants.
Sublingual tests involve putting a small amount of the suspect substance under the tongue, and then waiting to observe symptoms.
These look for Type IV allergies, or delayed reactions. They are very useful for skin symptoms and problems with the digestive tract, where a prick test has been negative but symptoms still occur with consumption of the food. The food extract is suspended in 90% dimethylsulfoxide, and applied to the skin in a special device - which is taped on and left for 24 to 48 hours. The results of the test have to be interpreted, to decide whether the reaction is contact dermatitis or due to an irritant. The test has proved accurate in 67% of children with acute symptoms after drinking milk, and 89% of children with delayed symptoms after drinking milk; however, the 1996 studyinvolved only 183 children.
There are various blood tests that are useful for identifying food allergies. RAST (RadioAllergoSorbent Test) checks for levels of IgE in the blood. ELISA (Enzyme Linked ImmunoSorbent Assay) checks for IgE, IgG and IgG4. FAST (Fluorescence AllergoSorbent Test) identifies allergens in which the indicator reagent is a derivative of flourescein, which emits polarised light. The RAST and ELISA tests are available via YorkTest in the UK.
Blood tests look for levels of IgE in the blood against specific allergens. The grading method varies according to the laboratory carrying out the test, but generally the higher the level of IgE, the stronger the allergic reaction. They are useful when people have been taking antihistamine medication (which can cause a false negative result for a skin prick test), if you have severe eczema, or are at risk of anaphylaxis (since the testing method does not involve direct contact with the allergen). Blood tests have traditionally been considered less accurate than skin tests, but newer methods, for example the CAP-RAST test, are more sensitive
It should be made clear that no IgE blood level, regardless of how low it is, completely rules out a food allergy diagnosis; the IgE taking part in the reaction may be attached to the mast cells rather than floating in the blood. The value of blood tests lies in their ability to give directions in the search for food culprits.
The ELISA test, for IgG food intolerances, has been validated by: the British Allergy Foundation, in a study of the YorkTest FoodSCAN test; by York University and separately by a study by the University of Manchester.
Other blood tests include:
• The Cytotoxic Test, which looks at the blood’s reactions to a variety of substances under the microscope, and is very much dependent on the laboratory technician for accuracy.
• The Cellular Allergy Test, which measure leukotriene responses to foods, and checks for intolerances as well as allergies.
• The SigA test, which will confirm that the gut lining is irritated, but not which food is causing the problem.
All of the commonly eaten foods are avoided for a period of one to three weeks, and then introduced individually while their affect on health is assessed. Different doctors have different ways of approaching elimination diets: some suggest a complete fast to begin with, while others are more flexible in their approach. For a week the patient may feel completely and utterly dire, but then a fairly spectacular improvement is often seen. If, after three weeks, there has been no improvement, it is generally a good idea to abandon the diet.
With food intolerances, as opposed to allergies, a longer period of strict elimination is necessary before the food challenge. Otherwise the patient may be immune to an immediate reaction due to intolerance, and only show allergic reactions.
Food challenges should only be carried out under medical supervision, particularly when the patient is a child.
This is the most thorough way of finding whether food is causing a reaction, but it is very time consuming and expensive. Under medical supervision, usually at a clinic, the patient is given two meals that look and taste identical; however, only one contains the allergen. Alternatively they may be given a series of capsules, some of which contain the suspected food, and others of which contain the placebo. Neither patient nor doctor may know which contain the suspect food, and which contain the placebo. If there is a chance that the allergy is serious, or that it may cause anaphylaxis, then adrenaline and other resuscitation equipment must be available. For people who may have multiple food allergies it can take a great deal of time to work out which are the culprits.
Histamine is a key mediator in inflammation, and very useful when the body is trying to protect itself from invaders. Some people, however, will release histamine from mast cells when eating certain foods and food additives: it all depends on how tolerant you are. Tolerance can be reduced by disease, particularly allergy and autoimmune disease, and various medications; the enzyme system that breaks down histamines can’t keep them at a ‘normal’ level. Too much histamine can cause stuffy, runny noses, irritated eyes, hives, swelling, general itchiness and headaches.
Some foods contain large amounts of histamine, and eating them can cause a similar amount of discomfort as a false food allergy. Histamine is formed in food by various bacteria, and is present in particularly large quantities in fermented foods, such as alcohol, cheese, salami and vinegar. It is also present in tomato, eggplant and spinach, citrus fruits and dried fruits, and various additives, and can be present at raised levels in fish that has not been gutted promptly.
Raised histamine levels are dealt with fairly well by the liver, and symptoms will not often last beyond 12 hours. Some drugs reduce the liver’s ability to do this, and viral hepatitis and cirrhosis of the liver can also make it harder for the body to detoxify histamine. Leakiness in the gut can increase susceptibility to histamine in food, simply because more histamine is allowed through. Asthmatics, in particular, may have difficulty in neutralising histamine in foods.
Other foods encourage the release of histamine: egg whites, shellfish, strawberries, tomatoes and chocolate are guilty in this respect.
Foods containing histamine
• Red wine, champagne, dessert wine, white wine, rosé wine, sparkling wine (listed from most histamine to least histamine)
• Beers (including non-alcoholic)
• Ripe cheeses (for example, Emmenthal, Gouda, Brie)
• Continental sausages (the ones that get cured for years and years)
• Oily fish (e.g. tuna, mackerel) that is not cooked or canned promptly
• Pickled foods
Other tests
The accuracy of these tests has not been proven, but they are popular, because they are non-invasive and offer a quick and easy “diagnosis”.
Kinesiology uncovers imbalances by testing the response of muscles to certain influences. It uses a mixture of chiropractic muscle information and Chinese energy flows. The theory suggests that certain foods can interfere with the energy flows in the body, and hence interfere with muscle function. The food is introduced under the patient’s tongue or held in a glass vial in the patient’s hand, and the practitioner tests the strength of the other arm in resisting downward pressure. The lower the muscle strength, the more a particular food is thought to affect health. With a skilled practitioner it can be helpful in identifying foods for further investigation, but an unskilled practitioner can be useless. It has not been investigated in a clinical trial.
This is a very popular test, and is offered via Holland and Barrett health stores in the UK. It uses a method of electro-acupuncture that uses ‘energy waves’ to assess reactivity to foods and other allergens held in a vial which is in an electric circuit with a meter to measure the degree of reactivity and a detection device, generally attached to a finger. A drop in current signifies an allergy or intolerance. The relationship between a positive result and the existence of an allergy or intolerance has not been proven in a clinical trial
The only information I can find out about this is that it may involve using a dowsing rod over a sample of hair; or that some chemical process is carried out. Bearing in mind that hair is dead protein, and, in the western world, has often been subjected to extensive chemical processes, it is hard to see what scientific value this could have
In many cases, you may be able to persuade your GP or family doctor to send you for further investigations.
An Online Database Specialist INfo, of UK Consultants and GPs may well provide an idea of what's available in your own local area.
Allergy UK has lots of information about specific allergies and how to go about getting tested, and printable factsheets to help you decide what the next step should be. However, in all cases you should refer to your GP first, before spending money on private treatment (in the UK).