Methods of Allergy Screening
The range of Allergy testing is enormous and surrounded with much controversy. Some tests claim to be scientifically validated while others have no scientific basis whatsoever. With no clearly definitive standard, allergy screening can be a minefield for sufferers.
The double-blind placebo-controlled food challenge test is conventionally considered the ‘Gold Standard’ for allergy testing. Other types of challenge tests include the inhalation and conjunctical tests. The patient is required to eliminate suspected foods (for up to two weeks), if symptoms disappear the foods are reintroduced one at a time in the form of a capsule or liquid with equal the amount of placebo (1). If symptoms develop in response to the food capsules but not the placebo then an allergy is detected.
This should be done under medical conditions as there is a risk of anaphylactic shock. Apart from the obvious discomfort the patient may feel if a reaction does occur, there are questions regarding the quantities of food in capsules and whether they are sufficient to stimulate an immune reaction. Although it does allow assessment of an individual’s reaction to the various allergy mechanisms, patient compliance may be low and we cannot asses what is going on internally or at a biochemical level. Scoring patient’s reactions or sense of wellbeing is fraught with difficulty, so interpretation of results may also be difficult.
The skin prick test is usually the first test recommended by doctors because it is simple, quick and inexpensive (1). The skin on the patient’s inner forearm (or back) is coded to indicate drops of solution containing known allergens, and then the skin beneath each drop is pricked with a lance so the solution can reach mast cells. If a wheal and flare reaction occurs, it happens within 20-30 minutes demonstrating an IgE reaction. A negative reaction is when the skin remains normal. An allergy can only be confidently diagnosed if clinical symptoms correlate with the allergens that tested positive. Not all allergies can be identified through this method and testing food allergens is less reliable than testing other allergens such as dust and pollen (1). Skin tests may be uncomfortable and there is a risk of anaphylactic shock or painful reactions that could leave scars. Up to 25 allergens can be tested at any time (1) but validity of testing depends on the quality of execution. Establishing sensitivity and specificity of allergic reactions is also difficult.
The skin patch test may be used to find out if a rash comes from direct contact with an allergen. Contact dermatitis is more commonly an occupational allergy (e.g. detergents, nickel, shellfish). Small amounts of prepared allergens are placed on discs which are then placed on the skin, often the back. The skin is then covered with a watertight bandage for 48 hours. When the discs are removed, the skin reactions are measured to assess any allergic reaction. Interpretation of results can be difficult (1), and testing is usually performed by dermatologists who may have more success determining between an allergic reaction and an irritant reaction. A standard European Battery panel of 22 allergens is used (2), covering a range of materials from medicaments to dyes and rubber.
An Endoscopic Study is conventionally used for the diagnosis of Coeliac disease and inflammatory bowel conditions. It involves swallowing a small camera mounted on a flexible tube and may involve biopsy or a provocation test, which is when allergens are applied directly to the mucosal wall and monitored for wheal and flare reactions.
This testing method may also be used for medication allergies. It is the most invasive of all the tests and there are risks of developing complications. An experienced endoscopist is required and sedatives may be used.
The Radioallergosorbent test (RAST) is a blood test used to measure the blood level of IgE antibodies produced in response to a particular antigen. Some laboratories use the Enzyme-Linked Immunosorbent Assay (ELISA) technology to determine which allergens the antibody reacts with, as it is more sensitive than the RAST procedure (3).
This test is thought to be more accurate than skin testing because it can measure the exact amount of allergen antibody in the blood (1). However, IgE should be bound to mast cells, if it is found free in the blood there needs to be large amounts of this antibody present. Even if the test is negative there is still a chance there may be an allergy (4) because: 1) all the IgE is bound and 2) other mechanisms (apart from IgE antibodies) are involved in allergic reactions. The level of antibody present does not correlate with the severity of an allergic reaction (4), and there is no indication of current allergencity, someone who has outgrown an allergy may test IgE positive for many years afterward (4). This type of test may be beneficial for people who cannot have skin tests (e.g. patients with dermatitis or taking certain medication). Some laboratories now offer a combined IgG and IgE RAST tests (3). Like others, this test is limited because it will only detect reactions to the allergens tested. Blood tests are invasive but probably less traumatic than some of the previously mentioned tests.
The Food Allergen Cellular Test (FACT) is a blood test that measures the release of chemical mediators from white blood cells once they have been stimulated and incubated with food allergens (5). Blood leukocytes release leukotrienes and histamine which are the chemical mediators responsible for some of the symptoms associated with an allergic response (6). This test measures the chemical mediators that are a result of these processes and it is therefore theoretically capable of detecting a range of reactions involved in both immediate and delayed type allergic responses, which are both IgE dependent and independent (6). Unlike RAST the test not only indicates which foods the cells are sensitive too, but also to what degree (6). More than 200 foods can be tested (5) and both allergies and intolerances may be identified. This is the test currently used by Michelle to detect allergy and intollerance.
Vega Testing involves measuring electromagnetic conductivity in the patient using a galvanometer (Wheatstone bridge circuit). A probe is held in one hand connected to the Vega machine while the other hand is tested with the machine’s measuring stylus. It tests resistance over an acupuncture point to different homeopathic preparations of foodstuff. The degree of allergy is interpreted by assessing the degree of distortion or ‘weakness’ recorded on the ammeter of the machine.
This method of allergy testing is very popular, however there have been no valid clinical trials (1) and there is no evidence to support the theoretical basis or the practical claims of the Vega test method (12). Even the inventor of the Vega machine Dr. Schimmel wrote ‘the effective base of the Vega test method is still unknown..’ (12). Although this technique has not been accepted by conventional medicine, some of the electronic screening devices have met standards required for U.S. Food Drug Administration (FDA) approval as an investigational device (3). The British Medical Association interestingly recommends that Vega testing should be avoided because the elimination tests often prescribed as a result of Vega testing should only be prescribed by a qualified nutritionist or dietician (1).
Applied Kinesiology & the DRIA test is a form of muscle testing which allows the body to communicate what it knows to the practitioner (3). There are numerous variations to the test, one example is when the patient raises an arm and keeps it perpendicular to the body, while holding a glass tube with the suspected food in the other hand. The tester assesses the strength of the raised arm by pressing on the patient’s wrist; any weakness is linked to a problem with the suspected food. The DRIA test measures muscle force with a special device called Driaton™.
This is also popular, but the many subjective factors make validity and accuracy of testing problematic. A review of 20 published research papers by the International College of Applied Kinesiology concluded that because “none of the papers included adequate statistical analysis, so no valid conclusions could be drawn from their findings.” (13). We may not be able to prove how it works (are we even testing the right indicators?), but there is a growing demand for kinesiology practitioners who would tell you that it does.
Other tests of unproven value include the Auricular Cardiac reflex method, a form of pulse testing which involves shining a light through a patients’ hand and assessing the pulse amplitude. Pulse tests that involve keeping charts of pulse recordings and assessing them for allergies. Hair mineral analysis measures mineral status and is sometimes incorrectly used for allergy detection.
(1) Brooks P (2001). The Complete Guide to Allergies. Constable, London.
(2) Fitzgibbon J (1998). Could it be an allergy? Gill & Macmillan, Dublin.
(3) Golan R (1995). Optimal Wellness. Ballantine, New York.
(4) Lab tests Online (2002). Allergy Test. www.labtestsonline.org
(5) Individual Wellbeing Diagnostic Laboratories (2003). Practitioner guide to Laboratory Services. New Malden.
(6) Abraham N, Berni-Klerck L, Sharma R, Gaier H (1999). The use of a cellular mediator Release Assay (FACT), for the Identification of Food Sensitivity in Clinical Practice. Individual Wellbeing, London.
(7) de Weck A, Stadler B, Urwyler A, Wehner H, Buhlmann R (1993). Cellular Allergen stimulation test (CAST) – a new dimension in allergy diagnostics. ACI News 5/1.
(8) Morris A (2003). Controversial Allergy tests. www.allergy-clinic.co.uk
(9) National Institute of Allergy and Infectious Diseases (1999). Food allergy and Intolerances. www.niaid.nih.gov
(10) Fell P, Soulsby S, Brostoff J (1991). Cellular Responses to Food in Irritable Bowel syndrome – an Investigation of the ALCAT test. Journal of Nutritional Medicine 2, 143-149.
(11) Eaton K (1992). Single dose level intradermal skin tests are not diagnostic in food intolerance: a double blind study. Integrated Therapies.
(12) Katelaris C, Weiner J, Heddle R, Stuckey M, Yan K (1991). Vega testing in the diagnosis of allergic conditions. Medical Journal of Australia. www.mja.com
(13) Klinkoski B, Leboeuf C (1990). A review of the research papers published by the international College of Applied Kinesiology from 1981 to 1987. PubMed ID:2351880