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Overview of Food Allergies
Michelle E. Conroy, MD Instructor, Dept. of Medicine
Massachusetts General Hospital April 10, 2013
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I have no professional conflicts of interest to disclose.
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Food allergy is big…
… and folks in the United States are impressionable!
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NCHS Data brief, 10/08
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? Incidence
Allergy 2005: 60 (Suppl. 79): 19–24
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What does “Food allergy” mean?
A food allergy is defined as an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.
A food is defined as any substance—whether
processed, semiprocessed,or raw—that is intended for human consumption, and includes drinks, chewing gum, food additives, and dietary supplements.
NIAID Guidelines, 2010
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First things first…
Toxic Non-Toxic
Food poisoning
Immune-Mediated Non-Immune Mediated
IgE-Mediated Non-IgE-Mediated
Lactase deficiency Reflux Sensitivities
Eczema Urticaria Anaphylaxis
Enterocolitis Proctocolitis
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The importance of the history
Allergy can almost always be diagnosed by a good history Start with scan for “atopic background”
Detailed account of “reactions” What was eaten? (sounds simple…) Amount/route of food ingestion/exposure Timing after ingestion Symptoms Relieving factors Recovery Prior similar episodes
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Non-immunologic mechanisms (mostly)-Sensitivities
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Mixed immunologic mechanisms- Eosinophilic esophagitis
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IgE mediated reactions- Anaphylaxis
Lancet 2008;371,9623:1538-1546
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WHAT WAS EATEN?
Major allergenic foods (>90% of allergies) Milk Egg Soy Wheat Peanut Tree nuts Shellfish (sesame)
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What happened??
Toxic Non-Toxic
Food poisoning
Immune-Mediated Non-Immune Mediated
IgE-Mediated Non-IgE-Mediated
Lactase deficiency Reflux
Anaphylaxis Urticaria Eczema (?)
Enterocolitis Proctocolitis Eosinophilic gastroenteritis
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What IgE does…
Mast cells immediately release:
Histamine
Heparin
Proteases
ANAPHYLAXIS
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What IgE does…
So we go looking for it….
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Skin prick testing
95% negative predictive value
50% false positive rate Context/selection Immediate, visual results Blocked by common
medications
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Skin prick testing
Measure presence of allergen specific IgE
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Serum Specific Food Allergy Testing
Yields a quantitative value…
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Serum Specific Food Allergy Testing
-Undetectable level has a LOW negative predictive value
If suspicious, confirm with skin testing About 50% false positive rate Interpretation can be difficult (i.e. need to wait at least 3-4
weeks post reaction to avoid false negative results) The big issue: Age and allergen specific values
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Food specific IgE levels
J Allergy Clin Immunol 2001; 107: 891-6
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Food specific IgE levels
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Age specific values
J Allergy Clin Immunol 2001; 107: 891-6
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Food specific IgE testing
Recall: 50% false positive rate!! Critical to test only for foods of high suspicion
based on history Unless you’re comfortable telling a patient to eat the
food for which there is a “positive test”
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Helpful overview of foods
Lack G. NEJM 2008; 359 (12): 1252-1260.
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More on cross reactivity
Spectrum paper
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AVOIDANCE/RESTRICTION
At the moment, the most accepted therapy Difficult! Give resources Anaphylaxis actions plan Please… (begging here)… prescribe Epi!!!
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Risk for fatal anaphylaxis related to food
On review of 32 fatalities: Both sexes equally Adolescents and young adults Peanut and tree nut allergy caused 94% of these fatalities Asthma Delayed administration of epinephrine
10% of these people had epinephrine with them
J Allergy Clin Immunol 2007
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Future directions
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Thank you for the invitation
Lots more to discuss…