Allergy Testing Flashcards
What are the four different types of allergy tests?
immediate hypersensitivity skin testing, serum IgE antibody testing, nasal smears for eosinohils, delayed hypersensitivity skin tests (patch testing)
What are the two most common food allergens for anaphylactic rxns?
peanut and seafood
During what season are tree and grass pollens common?
spring
During what season are weed pollens common?
late summer/fall
What does a personal or family history of atopic disease put someone at risk for?
allergies
What diseases are included in the atopic triad?
allergic rhinitis, eczema, asthma
What is atopy?
tendency to be “hyperallergic”
What are indications for allergy testing in someone who has rhinitis?
Symptoms not controlled by medications and allergen avoidance
What are indications for allergy testing in someone who has asthma?
Persistent asthma in patients exposed to perennial indoor allergens
What are indications for allergy testing in someone who has a suspected food allergy?
Previous suspected systemic reaction to food
What are indications for allergy testing in someone who has a suspected drug allergy?
Previous suspected systemic reaction to drug, and clinical indication for suspected drug
What are indications for allergy testing in someone who has a suspected insect sting?
Previous suspected systemic reaction to insect sting
What disease conditions is an immediate hypersensitivity test used to diagnose?
allergic rhinitis, allergic asthma, food allergy, penicillin allergy and stinging insect hypersensitivity
Who is at high risk for anaphylaxis during an immediate hypersensitivity skin test?
Poorly controlled asthma and reduced lung function. History of severe reactions to small amounts of allergen. Significant cardiovascular disease and elderly patients
What kind of allergy testing should be done if patients can’t have a hypersensitvity skin test?
immunoassay allergy testing
Why are beta blockers and ACE inhibitors contraindicated for skin tests?
they mask symptoms of anaphylaxis
Why might a skin test yield false negative results?
mast cell refractory period
Why should patients who have skin conditions (dermographism, urticaria, and cutaneous mastocytosis) not be skin tested?
false positive results are common
What is dermatographism?
caused by mast cells in the surface of the skin releasing histamines without the presence of antigens, due to the presence of a weak membrane surrounding the mast cells.
What is mastocytosis?
group of rare disorders of both children and adults caused by the presence of too many mast cells
Why are skin tests typically not done for patients who are currently taking TCAs, muscle relaxants, or antimemtic druge?
these drugs would need to be stopped for up to 2 weeks. do serum testing instead
How would tacrolimus (Protopic) used to treat eczema, affect a skin test?
decrease skin reactivity, give false negative
What are benefits of skin testing?
Most rapid, sensitive, and cost effective testing modality for the detection of IgE-mediated disease
How is a positive skin test determined?
Wheal equal or larger in size to that associated with histamine control. Wheal diameter larger than 3mm (histamine control usually produces wheal about 3mm diameter
How do intradermal injections compare to percutaneous injections?
higher sensitivity but lower specificity
For what suspected allergens do you reserve intradermal injections?
venom and PCN when percutaneous tests are negative
What is there a greater risk of with intradermal injections?
systemic rxn
What are the general principles for the interpretation of a positive skin test?
result ONLY indicates presence of IgE specific to that allergen. You can be sensitized to something but that doesn’t mean it is an allergy
What is the only medication that skin testing has been standardized for?
PCN (penicillin)
How does the specific IgE (RAST) test compare to skin testing?
less sensitive, more expensive
When is the RAST preferable to skin testing?
High risk for anaphylactic reaction to skin testing.
Presence of interfering medications
What is the specific IgE (RAST) test?
a blood test that measures the levels of allergy antibody or IgE, produced when your blood is mixed with a series of allergens in the lab
What do nasal smears usually show in cases of allergic rhinitis?
predominance of eosinophils
What is a Wright stain used for?
to differentiate blood cells
What can a Hansel stain be used for?
to see if there is a predominance of eosinophils (stain red) or neutrophils (stain blue)
When is the most appropriate time to consider specific allergy testing?
if a patient would likely benefit from immunotherapy
What does any positive test for an allergy need to be confirmed with?
history of reactivity and in some cases allergen challenge to confirm
