Diagnosis of type 1 allergy.

Prof. Mohamed Osman Gad ElRab .College of Medicine & KKUH .

Introduction :

Many patients with various مختلفه clinical

problems are suspected to have an allergic disease , يعني

حساسيه عنده انه اعتباراتك من مريضحط جاك اذاهم المرضى هذوال : واغلب

e.g. . - itching skin rashes. - upper & lower respiratory symptoms . - adverse reactions to food . - adverse reactions to drugs,(antibiotics, local anesthetics, analgesics ).

- Establishing a correct allergy diagnosis help to

select appropriate therapeutic interventions for

the patient such as :

الحساسيه عالج انواع : اشهر - allergen avoidance مثيرات تجنب. الحساسيه

- medications .

- immunotherapy .

Major indications االستخدام دواعي. for allergy testing االساسيه

1. patients with rhinitis in whom symptoms

are not controlled by medications .

allergic rhinitis .( IgE- mediated ). ( اللي هو النوع هذاللعالجات يستجيب ما اللي هو النوع وهذا االختبار بعمل عنه نبحث( العاديه

non-allergic rhinitis .( non IgE- mediated ) .

infectious . aspirin hypersensitivity. non-specific.

Prevalence االنتشار : معدل

60 – 70 % of rhinitis patients have

allergy ( IgE- mediated ).

25 – 34 % of patients with rhinitis develop

asthma within 10 years .

2. patients with persistent دائم symptoms of asthma .

58-80% of asthma patients have immediate skin test reactivity .

.(Kalliel etal. Chest 1989,96:1336-40).

58% of adult asthmatic patients in Riyadh have immediate skin test reactivity & specific IgE to prevalent منتشرهallergens.

(Gad EL Rab M.O., Annals of Saudi Medicine.1999,19:447-49 ).

It is recommended that all asthma patients

,who require daily therapy ,be evaluated for

allergens as possible contributing مساهمه factors .

Guidelines for the diagnosis and management of asthma : expert

panel report NIH publication no.98-4051,Bethesda,Md.,1997: 43,45

3. patients with suspected food allergy .

- adverse reactions to food proteins are divided into : IgE- mediated non- IgE mediated .( food intolerance ). عدم

حليب مع مشاكل يواجهون اللي الناس بعض مثل الطعام تحملياااي ( ) الجمالت

- approximately 5-6 % of children (younger than 3 years ) and 1.5 – 2 % of the general population suffer from food allergic disease .

Diagnosis of food allergy is important because the mainstay الرئيسي : of therapy remains الدعم

1. avoidance of the incriminated المسببالفول ( ) من الناسحساسين بعض .foods للحساسيه

2. education to deal with inadvertent exposure اكل ( اكل واحد المفاجئه الحاالت مع للتعامل التعليمحساسيه ) يسبب انه درى . ما

4. patients with suspected drug allergy .

- reliable ودقيق allergy tests for drugs are فعالavailable only for penicillin and local anesthetics

الموضعي جدا . التخدير مهمه

- e.g. suspected reaction to penicillin .

prescribe له مضاد alternative antibiotic يوصفآخر . حيوي

5. suspected insect sting reactions :

previous suspected systemic reaction to insect stings . - identify insect . - advice immunotherapy. من الحشرات الن

على ( مب يعني بها التحكم يمكن ال التي الحساسيه مثيراتحشرات تاكل ما ( كيفك

- e.g. the honey bee & black fire ant are common causes of anaphylaxis.

بـ وتعالج للوفاه تؤدي ان الممكن من والتي المفرطه الحساسيهEpinephrine ( adrenalin )

Types of allergy tests :

1. Immediate- type hypersensitivity skin testing .

a. percutaneous route .( skin prick test ).

b. intradermal route .( injection of allergen

within the dermal layer ).

2. assay قياس for allergen specific IgE antibodies .

3. Bronchial challenge test .

( occupational asthma المفتعل ( الربو - expose patient to allergen and record symptoms.

4. Double- blind food challenge test .

provide definitive النهائي diagnosis of food allergy

when clinical certainty والتاكيد . is needed االعتماد

( because of the low specificity of the skin test

with food allergens ).مهمه

1. the skin prick test ( SPT ) (the most commonly used method ) .

1. rapid.

2. accurate دقيقه . 3. cheap.

4. safe procedure. اجراءات 5. highly reproducible .

نتائج تعطي

Principle المبادئ of the skin test :

when allergen extracts are introduced into the skin ,of a

previously sensitized individual , they

cross- link IgE molecules on mast cells which :

release mediators and produce :

- a local wheal and flare reaction .

Site for prick test الوخز : اماكن

• The inner (volar ( ) الباطن aspect of the (الراحهforearm.

Or :

The skin of the upper back.

عند فقط المكان هذا :يستخدم - in dermatitis of forearm .

- children with small forearms.

Contraindications استخدامه to skin prick موانعtesting:

Do not apply skin prick tests to patients when there is convincing history of anaphylaxis to the test allergens.

this is particularly important in :

Nut ( ) مكسرات .allergy جوز

latex النباتات بعض . allergy افرازات

horse allergy.

drug allergy .

severe food allergy.

1.Diffuse dermatological condition. او عرضمنتشره جلديه مشكله

2. Patient unable to stop medications .

( anti-histamines inhibit the wheal& flare reaction patients advised to stop the drug 3-10 days before skin testing ) ظهور الدواء هذا يمنع ما عشان

االختبار نتائج

Other contraindications:

3. during pregnancy.

3. poor patient cooperation .

4 .Severe dermatographism

فيزيائي مؤثر عن ناتجه ارتيكيريايطلع ( اللي مثل الدخان و الحك كثره مثل

حرام لبست . ( اذا

Interpretation ميكانيكيه . of the skin test تفسير

Positive control skin test ( histamine ) Negative control skin test (diluent )

( essential for correct interpretation) .

-15 minutes after application of allergen,

examine test site for a wheal and flare .

- a positive reaction = a wheal 3 mm or greater in diameter + erythema .

Selection of allergens for testing .

- There are over 400 allergens known to cause allergic disease .

Selection is based on : 1.medical history .

2. prevalent المنتشره allergens in the area .

SPT is safe ,but the followingemergency resuscitative equipment must be

available :

* Injectable Adrenaline 1:1000. االهم * Oxygen .

* Oral Phenergan للهستامين مضاد & دواءinjectable.

* Hydrocortisone .

* Inhaled bronchodilator.

Number of allergens and age:

المثيرات * Any number from 1-40 allergens may be : عدد

tested in a single session .

* االشخاص أنه Consensus : عمر على ينص indicates االجماع

that the tests are of value from 4 months of age onwards .

However,

Infants & the elderly tend to have a less reactive skin.

الثاني :Multi – test device االختبار

.صينيه applicator in allergen tray غمس Dipأوال :

ثانيا : .Apply with pressure on the arm ثم

a positive test:

= 4.5 mm. wheal diameter.

( preferred by patients.)

احمرار ( ) حمره ينتج ال انه الحظ

السابق االختبار من اكبر القطر وان

Correlation بين : between العالقه

* size of skin test. * degree of IgE sensitization. * clinical symptoms.

90 % of patients with a wheal = 5mm.

react positive on provocation اثاره tests & the allergen tested is involved in clinical disease .

الثالث : : Intradermal test االختبار

used for investigating : يستخدمعن : للكشف

1 . insect sting allergy . 2. drug allergy .

hg

*High non-specific reaction rate.

الرابع . allergen - specific serum IgE test : االختبار ( also called RAST test – radioallergo-sorbent test )_

• Advantages:

1. No risk of reactions.

2. Not affected by medications.

3.Preferred in patients with high risk

of reactions:

-unstable asthma.

-anaphylaxis.

-sting insect allergy.

• Disadvantages :

1. Expensive.

2. Less sensitive than SPT.

3. Difficult to interpret الكشف in patients with high level of total IgE (1000 KU/ml )

Specific IgE (RAST) results are reported in classes :

class o : no specific IgE detected.

class 1 : low level .

class 2-4 : moderate level .

class 5-6 : high level .

Total serum IgE.

The spread of total IgE values is very wide

and reliable upper limits distinguishing

non-atopic and atopic could not be

established .

* Useful in large epidemiologic studies.

* Not applicable in the clinical evaluation

of individual patients.

Conditions with elevated total IgE :

These may include :

1. certain immunodeficiency disorders .

2. parasitic infections .

3. certain types of T-cell lymphomas .

4. atopic dermatitis .

5. eosinophilic lung disease .

Positive skin test reactions with no symptoms affect

8-30 %

These reactions may indicate :

1. past sensitization .

2. latent الكامنه allergy .

.

Prospective سابقه studies in Denmark showed that

30 to 80 % ( of asymptomatic patients with positive skin test become allergic depending on :

allergen exposure.

*have prognostic ( preventive) value.

Bodtger U; Current Opin Allergy Clin Immunl,2004;4(1):5-10.

Summary :

1. diagnosis of allergy determine line of

treatment e.g. avoidance of allergen,

immunotherapy .

2. skin test reactivity should be correlated مربوطمع

with clinical sensitivity .

3. definitive diagnosis of food allergy is by

double-blind challenge tests . مهمه

4. administration of allergy vaccines require

accurate identification of causative

allergens .(immunotherapy ).