Food Allergy - Challenge Testing and Skin Testing

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Atopic or Allergic March:

Allergies change as one grows older. Often a child first develops Eczema, then Food Allergy, Asthma and Rhinitis. Many will outgrow Eczema, Food Allergy and Asthma by age 15 years. (Barneton & Rogers BMJ 2002, 324. 1376-9). View PDF Article

	Eczema – Peak age 1 month, subsides by 5 years.
	Food Allergy – Peak age 1 to 3 months, subsides by 14 years, but some may have symptoms into adulthood.
	Asthma – Peak age 5 years, subsides by 14 years, but some may have symptoms into adulthood.
	Allergic Rhinitis – peak age 8 years, persists throughout adulthood.

Food Allergy:

May be mediated by IgG or IgE antibodies. Skin testing is only for IgE. Challenge testing with the food is the best way to diagnosis. IgE stimulates the mast cell and releases Histamine and to a lesser degree Platelet Activating Factor (PAF). IgG stimulates the macrophage and releases PAF. Both PAF and Histamine increase vascular permeability and can cause anaphylaxis.

Reactions which may mimic food allergies:

	Food mixers that wear latex gloves: Sushi, Sandwich and Sub Shops, etc. The customer can react to the Latex.
	Flour can contain contamination with dust mites.
	Fish can be infected with bacteria. Proteus breaks down fish muscle and releases histamine. View Abstract

Young infants have an increased risk of food allergy – anything which prevents breakdown of food in the gastrointestinal tract (stomach and intestines).

	GI tract not mature. Newborns have decreased enzyme (proteolytic) activity in the gastrointestinal tract, an immature (underdeveloped microvilli) lining and lack of IgA and IgM in gut (exocrine) secretions. Some recommend not introducing solid foods till 4 to 6 months of age.
	Use of antacids.
	Birth by C-section prevents the baby from picking up mom’s flora (bacteria) which helps break down food.
	Maternal diet during pregnancy and lactation.

Peanut Allergy: Peanut allergy is a common and the most severe food allergy. 70% of peanut allergic children react to the first ingestion of peanuts. In these cases, the infants have been previously exposed to peanuts possibly by mother’s milk or by cutaneous contact with the peanut oil. The initial reaction does not predict the severity of future reactions. 52% will develop potentially life-threatening symptoms – throat tightness and angioedema, wheezing, chest tightness, noisy breathing, increase in heart rate. (Vander Leek TK, et al. J Pediatr 2000; 137:749-55) View Abstract

35% of peanut allergic children will cross react with another tree nut.

Other common food allergens which can cause severe life threatening reactions (anaphylaxis) are: Tree nut, seafood, finfish, milk, and eggs. Food additives are also common – carmine, spices and food gums. Reactions can also occur from benzoates used in diet soft drinks and canned vegetables, monosodium glutamate (MSG) on salad bars in restaurants and propolis, paraben (Vaseline Intensive Care Lotion). Health foods have also been reported to cause reactions. There have been three reports of anaphylaxis to bee pollen. Many reactions to “Bird Nest” soup.

Food – Food Cross Reactions: (Sicherer SH, Cross Reaction JACI 2001; 108:881-890) View PDF Article

	Peanut - 59% will cross react to hazelnuts or brazil nuts. (Also, in allergic patients between 23% to 50% to other nuts.)
	Walnut - 37% will react with cashew and hazelnuts
	Wheat - 20% will react with another grain
	Fish – 50% chance of reaction with another fish
	Shell fish – 75% will cross react to another shell fish
	Cows milk -- 92% will cross react to goat's milk but only 4% with horse
	Kiwi, avocado, banana -- 11 % will cross react with latex

Pollen –Food Cross Reactions:

	This can occur with cross reaction to antigens in fruits and vegetables. Cooking may prevent reactions.
	Pollen (birch and ragweed) -- 55% will react with apples, peaches, honeydew etc.

Diagnosis of Food Allergies:

Skin Testing: (Remember this only tests for IgE reactions.):

Intradermal testing (shots) is not recommended (Intradermal testing is not paid for by Medicare).

Skin Prick testing: Good for telling what you are NOT allergic to but not what you ARE allergic to (low positive predictive accuracy, good negative predictive accuracy). (Skin prick testing is not paid for by Medicare.

	For milk and eggs, the testing results are approximately 50% false positive but less than 5% false negatives. For peanuts, 70% false positive and 10% false negative rate. No correlation between skin test size and severity of reaction. (Sporik R, et al. Clinical Exp Allergy 2000; 0:1540-6) View Abstract
	Skin Prick testing to nuts – 46% of those tolerant to nuts had a positive skin prick test as only 0.5% of those clinically allergic to nuts had a negative test. (Clark at, Ewan PW. Clinical Exp Allergy 2003; 83 1041-45) View Abstract

CAP RASTs (ImmunoCAP Specific IgE blood test): This test also measures IgE reactions. (This test is also not paid for by Medicare.) Of patients who had a clear nut allergy, 22% had a negative CAP RAST test compared to 0.5% who were negative to Skin Prick Testing. Where patients tolerated nuts, 40% had a positive CAP RAST compared to 46% who had a positive skin prick test (Clark at, Ewan PW. Clinical Exp Allergy 2003; 83 1041-45) View Abstract

Challenge testing: Is the gold standard. (Approximately 3% false negatives and 1% false positive.) Best to go on an elimination diet then challenge. This produces the most marked reactions. Eliminate all processed foods since allergy to additives are common. Caveman diet is best. Only eat things that can be gathered or killed. Nothing processed. Food groups to be rotated during testing are as listed below:

	Proteins – meats
	Grains – Rice, wheat, corn, oats, barley
	Vegetables – Yellow, green, potatoes
	Fruits

Cafarelli C, Petroccione T (Lancet 2001 358:1871-1872) found a false negative rate of approximately 3% and a false positive rate of less than 1% to food challenge testing in children. View Abstract

Prognosis:

	Peanut Allergy: Rarely outgrown. But may outgrow if the initial reaction involves only the skin (Skolnick HS et al. JACI 2001;107:367-374). View PDF Article
	Soy, wheat, egg, milk – frequently outgrown.

Treatment: Best is to avoid exposure. Some research is being done on desensitization to milk and other foods. You must know how to handle a reaction. Ask your doctor for guidelines and many physicians will prescribe and teach patients on how to use an epi-pen injection device.

Fatal Food Reactions: The majority of patients knew of the allergy but had accidental exposure. Patients with asthma were at higher risk. (Bock SA, et al. JACI 2001, 107: 191-3) Of 32 cases of fatal anaphylaxis the causative agent was identified as:

	Peanut – 20
	Tree Nuts – 10
	Milk – 1
	Fish – 1

View PDF Article See Allergy Anaphylaxis

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