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Université de Montréal. Assessment of Allergy. Allergy testing. Presented by Sylvie Daigle , RN, BSc . Assessment of Allergy. The term " Allergy " Allergic reaction Assessment of atopy Skin or immunological testing. What is Allergy?. Also known as Hypersensitivity Disease.
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Université de Montréal Assessment of Allergy Allergy testing Presented bySylvie Daigle, RN,BSc
Assessment of Allergy • The term "Allergy" • Allergic reaction • Assessment of atopy • Skin or immunological testing
What is Allergy? Also known as Hypersensitivity Disease
Definition • The term allergy ( von Pirquet -1906), can be summarized as the acquired, specific, altered capacity to react. • From Greek words: allos "change, altered" +ergon "reaction, reactivity". • Acquired means prior adequate antigenic or allergenic exposure.
Allergy has increased Incidence of allergy has doubled in the last 20-30 years, why? • Less exposure to parasitic disease? • Lower rate of breast-feeding ? • Exposures to air pollution? • Exposure to allergens in town vs in the country • The "hygiene hypothesis"?
Classification of allergic reaction by Gell & Coombs * Type I Anaphylaxis (IgE) Atopic diseases (immediate) Type II Cytotoxic Autoimmune hemolyticanemia Type III Immune complex Farmer’s lung (IgG) Type IV Delayed allergySkin reaction to tuberculin First published in 1968 : «Clinical aspects of immunology
Assessment of Atopy • Clinical ⇨ essential for asthma management (in particular if pets at home, in relation to the pollen seasons, etc.) • Epidemiologic studies • Occupational investigation
Type I Hypersensitivity Detection • Skin Prick Testing, recommended to assess atopic status • RAST (ELISA), serum specific antibodies • Intradermal Skin Testing: more sensitive than prick testing but less specific, with risk of anaphylactic reaction; also, difficulty of interpretation (local trauma due to injection)
Skin Prick Test Widespreaded in the 1970s after its modification by J. Pepys • Advantages • Mechanisms • Technique • Interpretation • Factors affecting skin test
House dust mite Ragweed, tree pollen Pets Cockroaches Molds Occupational protein allergens Relevant allergens (ubiquitous, occupational)
Occupational protein allergens Many occupational agents cause asthma by sensitization • mostly high-molecular-weight proteins • some low-molecular-weight agents In the case of high-molecular-weight allergens , skin prick tests are the preferred diagnostic correlates of Ig-E sensitization
Advantages • Skin prick testing is cheap, rapid and accurate • High degree of specificity • Safe and painless • Wide range of allergens • Objective evidence of sensitization
Technique and reaction • Introduction of allergen extract into the dermis • Ig-E-mediated response • Allergen-induced wheal-and-flare reaction
Technique • Use the inner forearm • Mark the area to be tested (2 cm apart) • Place a drop of each allergen extract on each mark • Prick the skin through the drop • Use a new lancet/needle for each allergen • Negative (saline solution) and positive control (histamine phosphate, 10 mg/ml) must be included: to exclude false positive reactions (dermographism) and false negative reactions (intake of antihistamines)
Put drops of allergen Prick the skin through extracts on the skin the drop
INTERPRETATION • Read at their peak (15-20 minutes) • Measure with a millimeter rule • Largest + smallest of wheal and erythema 2 • The wheal is principally used (diameter) • What if the negative control is positive? • What if the positive control is negative? • The size of the wheal does not relate to the severity of symptoms
Common errors in prick testing • Tests too close together (< 2 cm) • Induction of bleeding, leading possibly to false-positive results • Insufficient penetration of skin by lancet leading to false-negative • Spreading of allergen solutions during the tests.
Causes of false-positive skin prick tests • Irritant reaction •Dermographism • Contamination of an allergen extract • Enhancement from a nearby strong reaction Causes of false-negative skin prick tests • Extract of diminished potency • Medications modulating allergic reaction • Diseases attenuating the skin response, e.g. eczema • Improper technique (no or weak puncture)
Factors affecting skin test results • Quality of the allergen extract (standardized) • Area of the body, wrist least reactive • Age, less reactive after 50 • Circadian rhythms do not affect the skin reaction • Drugs: short acting antihistamines inhibit the wheal-and-flare reaction for up to 24 h; long- acting antihistamines may affect reaction for up 4-5 days.
CONCLUSIONS •When properly performed, skin tests represent one of the major tools for diagnosis of Ig-E-mediated diseases. • Assessment of the atopic status of subjects is often included in epidemiological studies of asthma and occupational asthma because atopy is a risk factor.
Natural history of sensitization, symptoms and diseases in apprentices exposed to laboratory animalsD Gautrin, H Ghezzo, CInfante-Rivard, J-L Malo. Eur Respir J, 2001. Predictive value of specific skin reactivity for W-R symptoms Skin reactivity PPV 28% 30% 21% 30% 9% W-R symptoms Skin Nasal Ocular Nasal and/or ocular Respiratory before 21 18 14 17 9 same time 22 17 16 19 4 PPV of W-R RC symptoms for probable OA : 11.4%
references - Bernstein IL, Chan-Yeung M, Malo JL, Bernstein DI. Asthma in the Workplace. Francis & Taylor, 2006 - Middleton’s Allergy: Prinnciples and practice vol. 1,chap 38. - Pepys, J. Clinical allergy, 1973, pp 491-509. - Pepys, J. Atopy: a study in definition. Allergy 1994;49: 397-399 - Bernstein DI and al.Characterization of skin prick testing responses J Allergy Clin Immunol 1994; 49:498-507 Web sites of interest - www.asthma-workplace.com - www.asthme.csst.qc.ca/document/Info_Gen/AgenProf/ - www.remcomp.com/asmanet/asmapro/index.htm