Diagnosis of Food Allergies - Skin testing, Blood tests, and unproven/dubious tests
Picture of skin test result, showing the typical wheals that show up
with allergies. Results are available in about 15 minutes. These
wheals usually go away on their own in less than 1 hour.
Skin testing is generally considered the test of choice in the evaluation of food allergies because it is a quick, accurate, nearly
painless procedure. It can easily be performed in the clinic setting and provides answers in less than 20 minutes. This test is
minimally intrusive and is well tolerated by young children (as young as 1 month of age), as well as adults!
To perform a skin test, drops of allergen extracts are placed on the forearms or the back and subsequently pricked with a plastic
device or a small needle. This feels like someone is pressing the tip of a pen or pencil onto the skin. There is no bleeding.
Allergies reveal themselves as red, itchy, mosquito like bumps called wheals. These itchy spots typically go away on their own in
less than an hour.
Antihistamines (to include Allegra, Claritin, Clarinex, Zyrtec, Benadryl, and Atarax) will inhibit the formation of wheals during skin
testing. It is thus important to stop all antihistamines 5-7 days prior to the day when the skin test will be done. Steroid nose
sprays (including Flonase, Nasonex, Rhinocort, Nasocort) and asthma medications (any asthma inhalers, and the pill Singulair)
have no affect on skin testing and should not be stopped prior to skin testing. Click here for a list of medications, including
antihistamines, that you should stop before an allergy skin test.
The strength of food skin testing is that it is inexpensive, easy to do, very well tolerated by even small children, is fast (results in 15-
20 minutes) and is very accurate when negative (95% accuracy). The weakness of the food skin test is that up to 20% of positive
tests can be false results, perhaps due to the food irritating the skin. Thus, skin testing is an excellent tool to rule out a food
allergy, but a positive test needs to be interpreted with caution. While the size of the wheal is not predictive of the severity of a
reaction to foods, the size of the reaction is predictive of the chance of a reaction. The bigger the wheal, the more likely a reaction
will occur - therefore, skin testing is also helpful to help assess if a food allergy is going away.
One way to evaluate for food allergies is with a blood test called a RAST (RadioAllergoSorbent Test). This test works by
measuring a sample of blood in a lab for allergy antibodies to selected foods (or other allergens, such as pollens). Results are
usually given as a number from 0 to 100. The higher the number, the more likely that an allergy is present. The severity of a
reaction, however, does not correlate with the numbers. That is: someone with a very high number will not necessarily have a
worse reaction than someone with a lower number. There are several different laboratory companies that have developed their
own RAST system (ImmunoCap, Immulite, Turbo RAST,...).
Is This Test Any Good?
RAST testing is generally less sensitive and more expensive than skin testing. For example, a recent study tried to assess how
good three different types of RAST were by looking at the results of 60 individuals with known peanut allergies. The ImmunoCap
and Immulite both missed 17% of patients and the Turbo RAST missed 15% of peanut allergic patients. In the same study, all
three RAST systems also missed 15% of soy allergic individuals tested. Similar to the skin test, up to 20% of results can be
falsely elevated. It is thus important to interpret RAST results carefully.
How Can the RAST be Useful?
One promising use of the RAST is to help assess when someone is outgrowing their food allergy. If the RAST values decrease
over time, there may be a chance that the individual is outgrowing their food allergy. Several studies evaluating children with food
allergies revealed that certain cut-off values could be helpful in determining if someone with a particular food allergy would react to
a food challenge or not. The problem is that the cut-off values are not only different for each food, but also appear to be different
depending on the age of the person. Therefore, the blood test results need to be interpreted carefully, along with the results of
skin test and the help of a board certified allergist.
ALLERGY TESTS TO AVOID
A quick search for “food allergies” on the Internet will lead you to hundreds of sites offering all types of tests and miracle cures for
your ailments. Many of these are scams that been demonstrated to be ineffective. The following tests should be avoided
because research demonstrates they not proven to be valid:
Applied Kinesiology (muscle testing)
This testing method, first conceived in 1964, is based on the theory that abnormal body functions can be assessed with muscle
tests. Applied Kinesiology is claimed to be useful for the evaluation of allergies, liver problems, and nutritional deficiencies. The
diagnosis is made by assessing muscle strength - “good things” will result in strong muscles while “bad things” will result in weak
muscles. Once a diagnosis is made, the patient will be given a list of things to avoid and a variety of vitamins and other products
to take that will fix the problem. The fact is that studies demonstrate that Applied Kinesiology is not useful for the evaluation of
allergies and nutritional deficiencies as the results are inconsistent and unreliable. For more information on Applied Kinesiology,
IgG Antibody testing
People who offer IgG and IgG 4 antibody blood testing claim that these tests are useful for the detection of food allergies and
delayed food reactions which contribute to a variety of different healthy problems. However, there is absolutely no validity to
those claims. Studies show that there is no association between food IgG antibodies, food allergies, or other diseases. The
formation of food specific IgG antibodies is, in fact, a normal physiologic immune response: healthy individuals make IgG
antibodies to whatever foods they eat, and if they avoid the foods, the quantity of these antibodies decreases or goes away
completely. Unfortunately, unscrupulous people use this normal response to foods as a way to convince people that their test and
treatments are effective.
Other unproven or fraudulent allergy tests and treatments include: (clink on the link for the full scoop on these dubious
Nambudripad's Allergy Eliminination Technique (NAET) - a system of diagnosis and treatment based on the notion that allergies
are caused by "energy blockage" that can be diagnosed with muscle-testing and permanently cured with acupressure and/or
acupuncture and/or laser treatments.
Cytotoxic testing—also described as Bryan's test, the Metabolic Intolerance Test, or sensitivity testing, is touted to help find food
sensitivities that cause various conditions such as acne, arthritis, asthma, bedwetting, depression, learning disorders, and so on.
The Australian Society of Clinical Immunology and Allergy is another good source of information on finding out the facts behind
unconventional testing and treatments of allergies.
Updated 25 January 2010
Wood et al. Accuracy of IgE antibody laboratory results Ann Allergy Asthma Immunol. 2007;99:34-41.
Triano JJ. Muscle strength testing as a diagnostic screen for supplemental nutrition therapy: a blind study. Journal of Manipulative
and Physiological Therapeutics 1982;179-182
Kenny JJ et al. Applied kinesiology unreliable for assessing nutrient status. Journal of the American Dietetic Association 1988;88:
Ludke R et al. Test-retest-reliability and validity of the kinesiology muscle test. Complementary Therapy in Medicine 1994;9:141-
Allergy Diagnostic Testing: An Updated Practice Parameter. Annals of Allergy, Asthma, and Immunology 2008;100:S1-148.
Middleton's Allergy Principles and Practice, 7th Edition
Hong et al. Food allergy and eosinophilic esophagitis: learning what to avoid. Cleveland Clinic Journal of Medicine 2010;77:51-
Picture of a skin test being placed on the back of a small
child. The sensation is similar to someone pressing a pen
or pencil on the skin.