Allergies Flashcards
What percent of kids are affected by food allergies? What type of mediated rxns?
- 6-8%
- IgE (anaphylaxis) or non-IgE mediated rxns
IgE mediated rxns characteristics?
- typically rapid in onset (occur w/in minutes)
- skin
- GI tract
- respiratory tract
- anaphylaxis
8 most common sources of IgE mediated rxns (90%)
- cows milk
- eggs
- soybean
- wheat
- peanuts
- tree nuts
- fish
- shellfish
Which of the 8 most common sources of IgE mediated rxns usually (80%) resolve by age 5?
- cow’s milk
- eggs
- soybean
- wheat
Which of these common sources of allergies are usually lifelong?
- peanuts
- tree nuts
- fish
- shellfish
Characteristics of a non-IgE mediated rxn?
- occurs hours to days after exposure
- typically in infants
- can present as chronic skin conditions or most commonly manifests as GI sxs:
proctitis/proctocolitis
enteropathy
enterocolitis
Sxs of food induced allergic rxn (IgE and non-IgE mediated)?
- cutaneous: erythema, pruritus, urticaria, angioedema
- ocular: pruritus, conjunctival erythema, tearing, periorbital edema
- upper respiratory: nasal congestion, pruritus, rhinorrhea, sneezing, laryngeal edema, hoarseness, dry cough
- lower respiratory: cough, chest tightness, dyspnea, wheezing, intercostal retractions
- GI oral: angioedema of lips, tongue, or palate, oral pruritus, tongue swelling
- lower GI: nausea, colicky abd pain, reflux, vomiting, diarrhea
- CV: tachycardia (occasionally bradbradia cardia in anaphylaxis), hypotension, dizziness, fainting, LOC
Dx of food induced allergies?
- Hx
- physical
- skin prick test, allergen specific serum IgE, oral food challenge
- pts with large wheals from skin prick test or with high serum specific IgE are likely to have food allergy
- parent and pt reports of food allergy should be confirmed with testing as mult studies demonstrate 50-90% of presumed food allergies are not allergies
Tx of food induced allergies?
- avoidance
- epi-pen for tx for anaphylaxis
What sxs can be assoc with food allergies?
- atopic dermatitis
- acute urticaria
Relationship b/t atopic dermatitis (eczema) and food allergies?
- food allergy has been reported in up to 35% of pts referred to an allergist or derm for atopic dermatitis
- consider eval in infants and children with moderate to severe atopic dermatitis or if there is a hx of exacerbation when eating specific foods
- if food allergy is dx, the atopic dermatitis often improves after dietary elimination of that food
Relationship b/t acute and chronic urticaria with food allergies?
- the causes of acute urticaria vary and include infection, drug rxn, and food allergy
- acute urticaria is common sx present with food allergy
- in contrast, chronic urticaria is rarely related to food allergy
- food allergy testing is rarely indicated for chronic urticaria since most cases are idiopathic
What nasopharyngeal sxs occur with food allergies?
- acute rhinitis (typically assoc with other orpharyngeal sxs such as pruritus of throat and angioedema)
- chronic rhinitis is NOT a manifestation of food allergy
Most appropriate test in initial assessment of food allergy? Test results?
- serum specific IgE testing or skin prick testing
- a positive rxn is a wheal at least 3 mm greater than negative control
- neg predictive value is greater than 95% while the positive predictive value is less than 50%, therefore there are many false positive results
- antihistamines should be d/c prior to testing
- testing can’t be performed on skin with extensive eczema/rash or in pts with dermatographia
What is impt to remember about serum specific IgE testing?
- detection of serum IgE to specific allergens
- all positive and neg tests (skin and serum tests) need to be correlated with pts clinical hx
- a + test alone doesn’t make the dx of clinical food allergy (evidence of sensitization: immunological response)
Gold std for dx of food allergy?
- a double blind, placebo controlled food challenge. Open challenges are generally used in most clinical settings
- pts may benefit from oral food challenge if they have borderline test results or if false + or - is suspected based on clinical hx
- may prevent unjustified food elimination from diet
Oral food challenge process?
- pt given gradually increasing amt of suspected food allergen over a time period of hours to a day
- process requires close medical supervision
Atopy patch tests use?
- currently used to d delayed hypersensitivity T cell mediated rxns such as contact dermatitis
- atopy patch testing for IgE mediated food allergy isn’t recommended
What are variables in the skin tests and specific IgE tests?
- each allergen may have diff normal IgE level and wheal diameter
- also dependent on age of child
- cutoff value is the concentration of specific IgE for particular food allergen that is 90% predictive of clinical rxn to food
- increasing levels of specific IgE and wheal response to SPT correlate with allergy but don’t predict severity of rxn
Why should food be continued on a regular basis if positive IgE results with no rxn while consuming food?
- because testing indicates that the child is sensitized to the allergen, a prolonged absence of the food from the diet could lead to clinical sxs upon re-exposure
