Chapt. 5: Principles of Allergy Diagnosis Flashcards
Immediate-reading allergy skin tests address what type of hypersensitivity?
Type I. Can confirm sensitization to a specific allergen. They represent the primary diagnostic tool of IgE-mediated diseases.
The IgE-mediated allergic response in the skin results in an immediate wheal and flare reaction that which is followed by a late-phase reaction (LPR) starting how many hours after?
1-2 hours later, peaking at 6-12 hours, and resolving in approximately 24 to 48 hours. The LPR is represented by an erythematous inflammatory reaction.
What induces the immediate reaction after allergy skin test?
Mast cell degranulation
What is released after 5 minutes after allergen injection? When is the peak?
Histamine and tryptase. Peaks at 30minutes.
What is the major mediator of wheal and flare reaction?
Histamine.
Does the size of the wheal correlate with the concentration of histamine released?
No.
What has replaced the RAST (radioallergosorbent test)?
FEIA (flourescent immunoassay).
What are the three majorly important variables to interpret skin test?
Allergen extract used
Technique
Patient
This chemotherapeutic drug may illicit skin necrosis and their use should therefore be strictly avoided.
Vinorelbine
Can cause false positive reaction by non-immunologic mechanism
Hymenoptera venom
Can elicit a wheal and flare reaction in non-sensitized patients
Thimerosal
For skin testing with fresh foods, _________ of allergen by cooking has been well established.
Thermal denaturation
If tests are placed too close together _____, and overlapping reactions cannot be separated visually.
<2cm
Intradermal skin testing amount
=<0.1ml
Average volume of the prick-test inoculum
0.016 uL
Average volume injected into the dermis with intradermal test?
0.02-0.05ml
Concentration of allergen extract required to elicit a positive reaction with intradermal testing is __________ times smaller than necessary for a positive prick-puncture test.
1000-30000
Positive control solutions?
Histamine
Codeine phosphate
Mean wheal size for positive control
5-8mm
Positive control should optimally show a wheal diameter that is?
> =3mm
Interpreted as positive and possible indicative of a clinical allergy in prick-puncture test?
> 3mm wheal diameter and >10mm flare diameter. Another criteria is the ratio of the size of the wheal induced by the allergen compared to the positive control.
Allergic sensitization with no correlative allergic disease occurence?
8-30% of the population
_____ of sensitized-only individuals subsequently develop allergic symptoms?
30-60%
With inhalant allergens, the cheapest and most effective method to diagnose respiratory allergies?
Skin-prick test
First-generation H1 antihistamines reduce skin reactivity for how long?
For up to 24 hours or slightly longer (for >5 days for ketotifen).
How long do the second generation H1 anti-histamines suppress skin responses? (Azelastine, bilastine, cetirizine, desloratadine, ebastine, fexofenadine, levocetirizine, loratadine, mizolastine, rupatadine)
3-7days
This anti-histamine inhibits skin tests more than others, and this effect correlates with relief of allergic rhinitis symptoms?
Cetirizine
Topical H1 antihistamines which may suppress skin tests, especially if multiple doses are used, thus should be discontinued for at least 48 hours before skin testing?
Levocabastine or azelastine
This classification of antidepressants exert a potent and sustained reduction in skin response to histamine?
TCAs
What other medications have an H1 antihistaminic activity and can abrogate skin test responses?
Tranquilizers and antiemetic agents of the phenothiazine class
Abolishes skin reactivity after 1 to 3 days of therapy and for up to 11 days after its discontinuation?
Topical doxepin hydrochloride
What duration of administration of corticosteroids used at therapeutic doses in asthmatic patients does not modify cutaneous reactivity to histamine or allergens?
<1 week
How does long term corticosteroid therapy alter results of prick skin testing?
Does not alter histamine-induced vascular reactivity in skin but affects cutaneous mast cell responses and modifies the skin texture, which makes interpretation of immediate skin tests difficult in some cases.
Potential for interference from inhaled corticosteroids?
Insignificant.
Application of topical dermal corticosteroids for how long reduces the immediate and the late phase skin reaction induced by allergen?
1 week
Slightly reduces skin tests, but its administration does not need to be stopped before skin testing.
Theophylline
Effect of short-acting, inhaled B2 agonists in doses approved for the treatment of asthma effect on skin testing?
No effect
Effect of propanolol in skin testing?
Significantly increase skin histamine reactivity
Effect of inhaled cromolyn and nedocromil on skin wheal response to skin tests with allergens or degranulating agents such as topically applied sodium cromoglycate?
No effect
Effect of ACEI
Moderately increase skin reactivity to allergen, histamine, codeine and bradykinin.
Effect of topical pimecrolimus on skin sensitivity?
No effect
In how many minutes will a wheal and flare response be induced for histamine? for mast cell secretagogues? For allergens?
8-10 minutes
15 minutes
15-20 minutes
Immediate skin test how long to interpret?
Skin prick test?
Intradermal test?
15mins
20mins
Plays a key role in the LPR by generation and release of cytokines?
Lymphocytes, predominantly CD4 T cells
What plays a key role in delayed hypersensitivity reactions?
CD8 T cells
2 risks with skin prick testing?
Infectious and allergic
S. epidermidis can survive in allergen extracts for how long?
21 days
Overall rate of generalized reactions to prick-puncture test?
<0.5%
Risk factors for adverse reactions during skin testing?
low age and active eczema for generalized allergic reactions
female gender and multiple skin-prick tests performed on a single patient for vasovagal reactions.
No fatalities have been reported.
Incidence of systemic reactions in intradermal testing
0.02-1.4% of tested patients
In patients with history of anaphylaxis, use this test concentration to minimize untoward adverse local and systemic reactions.
Perform prick-puncture tests before intradermal tests and use serial 10-fold dilutions of the usual test concentration
Waiting period after intradermal test?
20mins in the office of the physician. May be extended for high-risk patients (e.g. patients treated with B-blocking agents)
How to manage in case of generalized anaphylactic reaction?
Apply rubber tourniquet above the test site on the arm and a 1:1000 aqueous epinephrine (adrenaline) solution administered IM, preferably in the lateral thigh (i.e. vastus lateralis)
Skin wheal test pattern?
Increase in size from infancy to adulthood and then often decline after the age of 50
At what age is a significant wheal detected using the prick-puncture test?
After 3 months of age.
How do infants react to a prick-puncture test?
Large erythematous flare and a small wheal
Routine repeated skin testing and serum IgE dosage is recommended in what clinical scenario?
Venom allergy immunotherapy.
What is more sensitive, the in-vitro allergen-specific IgE test or the skin prick-puncture test?
Skin test
What is the percentage agreement between the allergen-specific IgE test and skin prick-puncture test?
Between 85-95%
How long before practicing immediate-reading skin tests should H1 antihistamines be stopped?
1 week before practicing
Where can skin test be performed?
On the back or forearm (or both, at the same time)
What are the differences in reactivity of the back or forearm?
The middle and upper back are more reactive than the lower back, the antecubital fossa is the most reactive portion of the arm, whereas the wrist is the least reactive (therefore, tests should not be placed in the areas 5 cm from the wrist or 3 cm from the antecubital fossa)
Safety distance between 2 tests?
2 cm between tests
What is the Oral Allergy Syndrome?
“Birch-fruit-vegetable syndrome”, due to primary sensitization to the major birch pollen allergen Bet v 1 and its extensive cross-reactivity with its labile homologs in fruits, vegetables, and nuts
What is the Latex-fruit-vegetable syndrome?
Due to the cross-sensitization between the allergenic components present in natural rubber and similar epitopes present in fruits such as kiwi or banana
After a systemic allergic reaction, how long is the refractory period?
6 weeks
What is the reason for the refractory period after a systemic allergic reaction?
This cutaneous anergy (or hypoergy) is attributed to the mediators’ depletion after mast cell degranulation.
Are skin tests recommended in immunotherapy follow-up?
No, except for hymenoptera venom immunotherapy
The most convenient and least expensive screening method for detecting respiratory and food allergic reactions in most patients?
Prick-puncture tests
