Allergy Pathophys
first time allergy prone person runs across allergen they make large amounts of IgE against it.
These IgE molecules attach themselves to mast cells.
2nd time exposure the IgE primed mast cells release granules and chemical mediators (histamine, cytokines)
Chemical mediators cause symptoms of allergy.
Types of Allergy Tests
Immediate-Type Hypersensitivity Skin Test
*most rapid, sensitive, and cost effective
Specific Serum IgE aby test (RAST; radioallergosorbent testing)
Nasal smears (for eosinophils)
Delayed type hypersensitivity skin tests (patch testing) for contact dermatitis
Common Allergens
food; dairy, wheat, eggs, seafood, nuts
inhalant: pollen, dander, grass, trees, dust mites
Medication: abx, aspirin
Contact: metals, fragrances, dyes, plants
Clinical Hx: Triggers
outdoor symptoms are suggested by hx;
Spring: trees or grass pollen
Summer: grass pollen
Late summer/early fall: weed pollen, mold
Year round: mold
Indoor symptoms are suggested by hx:
molds
pets
dust mites, cockroaches
Atopy has the tendency to be?
Individual presents with….
be “hyperallergic”
presents w/: eczema, allergic rhinitis, allergic conjunctivitis, allergic asthma
*tendency to have food allergies
What are some indications for specific allergy testing?
symptoms of allergy (at any age)
-Respiratory symptoms; itchy eyes, nose or throat, nasal congestion, runny nose, wheezing
- Skin symptoms: urticaria (hives), pruiritis (itching), atopic dermatitis (eczema)
- remember, just because its indicated doesnt mean it needs to be done.
Indications for allergy testings in…
- Rhinitis
- Asthma
- Suspect food allergy
- Suspect drug allergy
- Suspect insect sting
R- symptoms not controlled by meds
A- persistent asthma in pt exposed to perennial indoor allergen
SFA: previous suspected systemic rxn to food
SDA- previous suspected systemic rxn to drug, and clinical indication for suspected drug
SIS- previous suspected systemic rxn to sting
Allergy test: immediate type hypersensitivity rxn
- how is this test performed?
- used most commonly to diagnose?
- pts w/ high anaphylactic rxn from test?
- CI
- medications that may affect skin test
- skin prick/scratch or ID
- diagnose allergic rhinitis, allergic asthma, food allergy, penicillin allergy, and stinging insect hypersensitivity
-anaphylaxis:
poorly controlled asthma and reduced lung function, hx severe rxn to small amount of allergen, CVD and elderly pt
CI- if high risk for anaphylaxis, recent anaphylactic event (*may result in false neg. for up to a few months), taking meds that may interfere w/ anaphylaxis tx (BP meds, Beta 1 blockers), or skin conditions that may skew results (psoriasis)
-meds: Hold H1 and H2 blockers, topical glucocorticoids, xolair, TCA, muscle relaxant, antimetic drugs
What is dermatographism?
skin sensitive to being scratched, mast cells in the surface of the skin release histamine w/o Ag present, histamine released and causes skin to swell in the affected areas.
Skin testing results are obtained after how many days?
What is the downside for the patient?
- results obtained same day
- downside is the pt needs to be motivated to do something with their results
Skin Prick testing
- how does this work?
- when to do this test?
- helpful in determining if positive or negative result?
- prick minute amount of allergen to see if local response
- most appropriate INITIAL test
- helpful in excluding allergy if test is neg. if test is positive that means it is POSSIBLE you have allergy to that allergen.
Intradermal Injections
- how do they compare to skin prick tests?
- used to test for which disease if skin prick in neg?
- greater risk for what?
- not used to diagnose what type of allergies?
- higher sensitivity than skin prick testing, though have lower specificity
- reserved for venom and PCN when skin prick tests are negative
- greater risk for systemic rxn (only performed after negative prick testing)
- food or latex allergy
What does a positive skin result really mean?
+ skin result ONLY indicates presence of IgE specific to that allergen, you can be sensitized to something but that doesnt mean its an allergy
Skin test is only validated for the evaluation of which medication?
penicillin allergy
Specific IgE (RAST) Testing - SItuations where this is preferable to skin testing
- high risk for anaphylaxis (those individuals would be poorly controlled asthma and reduced lung function, ppl w/ hx of severe rcn to minute amounts of allergen)
- Presence of interfering medications (such as beta 2 blockers and ACE inhibitors, may inhibit management of anaphylaxis)
How does the Specific IgE (RAST) test work?
blood test that measures the level of allergy aby or IgE produced when you blood is mixed w/ a series of allergens in the lab.
Nasal Smear
- types of stains used
- when might this test be especially clinically useful?
- wright(purple) and hansel (red)
- clinically useful in trying to determine whether a pt has rhinitis due to infection or allergen.
Are serum IgE and eosinophil counts useful in tesing allergy? Why or why not?
They are not useful in the majority of patients, dont check total IgE serum unless you have specific indication such as going onto xolair therapy.
You dont check this because it doesnt give you any information about what they are allergic to.
Skin patch testing (delayed type hypersensitivity)
- how does this work?
- identifies delayed type hypersensitivity rxns such as?
- patch placed on skin and worn for 48-72hrs, removed in follow up visit, and then follow up again in another 24-96hrs.
-contact dermatitis
(irritant contact dermatitis vs. allergic contact dermatitis)
Most important part of allergy assessment?
CLINICAL HX
any + test needs to be confirmed by clinical hx of reactivity
Atopic Triad
allergic rhinitis, asthma, eczema
*pts are much more likkely to have one if they have another…AND it provides clues if 1st degree family member has one of these.
Most important utility of a wright or hansel stain is..?
whether the etiology of rhinitis is in question. (allergic or infectious?)
Hansel- Eosinophils Red Neutrophils blue
If worried about anaphylactic rxn which type of skin test do you use?
Specific IgE (RAST) testing
