Chapt. 5: Principles of Allergy Diagnosis Flashcards by A M

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.

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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.

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What induces the immediate reaction after allergy skin test?

Mast cell degranulation

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What is released after 5 minutes after allergen injection? When is the peak?

Histamine and tryptase. Peaks at 30minutes.

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What is the major mediator of wheal and flare reaction?

Histamine.

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Does the size of the wheal correlate with the concentration of histamine released?

No.

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What has replaced the RAST (radioallergosorbent test)?

FEIA (flourescent immunoassay).

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What are the three majorly important variables to interpret skin test?

Allergen extract used
Technique
Patient

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This chemotherapeutic drug may illicit skin necrosis and their use should therefore be strictly avoided.

Vinorelbine

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Can cause false positive reaction by non-immunologic mechanism

Hymenoptera venom

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Can elicit a wheal and flare reaction in non-sensitized patients

Thimerosal

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For skin testing with fresh foods, _________ of allergen by cooking has been well established.

Thermal denaturation

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If tests are placed too close together _____, and overlapping reactions cannot be separated visually.

<2cm

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Intradermal skin testing amount

=<0.1ml

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Average volume of the prick-test inoculum

0.016 uL

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Average volume injected into the dermis with intradermal test?

0.02-0.05ml

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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

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Positive control solutions?

Histamine

Codeine phosphate

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Mean wheal size for positive control

5-8mm

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Positive control should optimally show a wheal diameter that is?

> =3mm

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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.

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Allergic sensitization with no correlative allergic disease occurence?

8-30% of the population

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_____ of sensitized-only individuals subsequently develop allergic symptoms?

30-60%

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With inhalant allergens, the cheapest and most effective method to diagnose respiratory allergies?

Skin-prick test

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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