Waipuna Conference Center
Friday 13 August 2010
Vincent St Aubyn Crump








Overview of Allergy Diagnosis
Skin Prick Test & Prick-Prick Test
ImmunoCAP Specific IgE
Comparison of the two with emphasis on the diagnosis & follow-up of Food Allergy
Penicillin Allergy
Atopy Patch test
Cases for Discussion

Pre-test Probability score
Specific- IgE Tests
 Skin Prick Tests
 Prick-Prick Test
 Serum IgE levels o Immuno-CAP (RAST)
Provocation Tests
 Oral Challenge
 DBPCFC
 Nasal & Bronchial Challenges
Test for Delayed Hypersensitivity
 Patch Tests o Contact Dermatitis o Delayed food reactions o Drug reactions




Is defined as the probability of the allergic disorder being present, before a diagnostic test result is known
Is useful in interpreting the results of all allergy tests
Is useful in deciding whether it's worth doing the allergy testing at all








Anaphylaxis* after eating known food allergen
Very good history temporally compatible with an IgE-mediated (Immediate) reaction
Reliable witness for reaction
Presence of objective signs of known IgEmediated reactions
Presence of Atopy (Asthma, eczema & hay fever)
1 of the 8 common food allergen implicated
No other non-allergic explanation for symptoms



The Likelihood Ratio (LR) is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.
LR positive = sensitivity / (1 - specificity)


LR negative = (1 - sensitivity) / specificity
LR is better than sensitivity & specificity because it is less likely to change with prevalence of disorder






IgE represents <0.001% of total Igs
Majority of IgEs are bound to surface of mast cells and basophils
~ 50% of patients with allergic rhinitis or asthma will have elevated IgE
Total IgE more often elevated in AD, and correlates with severity of AD
Total IgE also elevated in:
– Parasitic Infections
– Bronchopulmonary Aspergillosis
– Immunodefieciecy, such as HIV infections
– Cigarette smoking

Total IgE – Normal Reference Interval
Age (years) Range (IU/ml)
<1 1-52
1-4 0-352
5 – 10 0-393
11 – 15 2 – 170
>15 0 – 158

Very high levels of total IgE can give false positive Specific
IgE results (multiple allergens tested positive), due to nonspecific binding of IgE antibodies











To confirm atopy, assisting in the diagnosis of asthma, eczema in infants
– Especially differentiating transient wheezers in infancy from persistent / asthmatics
Before initiating immunotherapy
To monitor progress during immunotherapy
Acute Urticaria & Anaphylaxis
All asthmatics requiring therapy
Occupational Diseases including latex allergy
Eczema
Some drug reactions: Penicillin, some herbals such as Echinacea.
In an Australian study ~50 % of cases of allergy to Echinacea, were thought to be IgE-mediated, and skin prick testing was helpful in their diagnosis.
Stinging insect anaphylaxis
Rhinitis vs Sinusitis

 Skin Prick Tests are used to screen patients for sensitivity to specific foods
 Allergens eliciting a wheal of at least 3 mm greater than the negative control are considered positive
 Overall positive predictive accuracy is < 50 %
 Negative predictive accuracy > 95 % (negative skin test results essentially confirm the absence of IgE-mediated reactions)

 Sensitivity similar to skin prick tests (slightly less)
 Good correlation with other procedures
 Efficiency: Depends on the allergen
 Indicated if SPT are contraindicated (eg, skin disease, medications)
 Useful if discrepancy exists between history and SPT
 The use of quantitative measurements has shown to be predictive, for some allergens, of symptomatic IgEmediated food allergy

Feature Importance SPT
Availability ++++ ++++
Speed of results ++++ ++++
Sensitivity ++++ ++++
Specificity ++++ +++
Standardization +++ ++
Quantification ++++ +++ of results
Temp. Stability ++ +++
Reagent stability +++ ++
Drugs effects ++++ +
Educational ++++ ++++
CAP-RAST
++
+
+++
++++
+++++
+++++
++++
++++
++++
++

When should skin prick tests not be done or should be done with extra caution?







For mass screening in the general population. Up to
40% of adults will have positive skin prick tests to insect venoms, but only a small percent experience anaphylaxis to venoms. Having a positive skin prick test to a venom will not predict if that individual will get anaphylaxis, if stung by that insect
In presence of dermographism
Patient unable of unwilling to stop medications like antihistamines and some antidepressants
Allergy to fruits & Vegetables. Do prick-prick test instead
Within 6 weeks of an anaphylactic reaction.
If therapy for anaphylaxis is not readily available
Extreme caution in pregnancy

Drug Degree of supression Duration of supression
Loratidine ++ 3 – 5 days
Cetirizine ++ 3 -5 days
Phenergan + + 3 – 10 days
Astemizole ++ >1 month
Cimetidine 0 to + not significant
Ranitidine + not significant
Famotidine 0 to + probably not significant
Ketotifen ++++ > 5 days
Imipramines ++++ >10 days
Phenothiazines ++
Nasal steroids 0
Topical steroids 0 to ++
Systemic steroids > 2 weeks & > 20mg / day reduces wheal & flare
Montelukast 0
Cyclosporin 0
EMLA cream reduces the flare but not the wheal

Skin Prick Test Form



Practice name / Ordering physician:
Street address City
Telephone Fax
Patient name: ______________________________ Date of birth: __/__/__
Testing Technician: _______________________


Last use of antihistamine (or other med affecting response to histamine): ___ days medication __________________



Testing Date (s) and Time: Percutaneous __/__/_____________AM PM
Intradermal __/__/_____________AM PM
General information about skin test protocol
– Percutaneous reported as: Allergen: Testing concentration: Extract company (*see below)
Location: back__ arm___ Device: _________Intradermal: 0.__ml injected,
Location: arm Testing concentration: 1:___ w/v or BAU or AU/ml, PNU

– Results Longest diameter (Left in this example) or longest diameter and orthogonal diameter (Right in this example) of wheal (W) and erythema (flare) (F) measured in millimeters at 15 minutes
– Blank in results column indicates test was not performed, O=negative
* Extract manufacturer abbreviations:, STG= Stallergens, AK=ALK Abello, AD=ALK (Denmark), H=Hollister–Stier,
Allergen:Concentration: Skin Prick Test Allergen: Concentration: Skin Prick Test .
Extract Manufacturer. Wheal Flare *Extract Manufacturer. * Wheal Flare
Allergens (W) (F) Allergens: (W) (F) .

House dust mites Milk


Cat Egg
Dog Wheat








The wheal & flare should be recorded in millimeters
3 mm is considered the cut-off for positive, but may overestimate clinical allergy!
All results should be compared to the negative and positive control
If negative control is positive the patient has dermographism, and entire test is invalid
If histamine control is negative, the results are probably being inhibited by antihistamines (Patients do forget!)
In hyperpigmented skin the indurations might have to be palpated
Remember that sensitivity (positive skin prick tests) does not mean clinical reactivity or allergy .

Size of SPT wheal (mm) 100% likelihood of + Challenge
Milk Egg Peanut
Children: 0-2 years of age
>6 >5 >4
Children: all ages (medium =3 yrs)
>8 >7 >8
Note: Results may vary widely due to lack of standardization of
SPT (extracts, devices)
(Clin Exp Allergy 200; 30:1540-1546)

Food
Egg
NPV PPV
High Risk Low Risk High Risk Low Risk
90 %
Milk 90%
Peanut 75%
Soy 84%
Wheat 94%
Fish 80%
99%
99%
99%
97%
98%
99%
85%
66%
55%
35%
35%
77%
17%
2%
15%
12%
15%
30%







RAST (radioallergosorbent test) invented and marketed in 1974
The suspected allergen is bound to an insoluble material and the patient's serum is added
If the serum contains antibodies to the allergen, those antibodies will bind to the allergen
Radiolabeled anti-human IgE antibody is added where it binds to those IgE antibodies already bound to the insoluble material
The unbound anti-human IgE antibodies are washed away.
The amount of radioactivity is proportional to the serum IgE for the allergen



In 1989, Pharmacia Diagnostics AB replaced RAST with a superior test named the ImmunoCAP Specific IgE blood test
Also describe as CAP RAST or CAP
FEIA (fluoroenzymeimmunoassay)

Food Specific Ige (immuno-CAP RAST) values at /or above which there is a 95% risk of
Clinical Allergy (no challenge necessary)
Food___ _Serum IgE (kIU/L) for 95% PPV


Egg (child) >7
Egg (age <2 yr) >2


Cow’s milk (child) >15
Cow’s milk (age <2 yr) >5


Peanut >14
Fish >20


For animal and mould allergens, a high proportion of positive skin test results were disregarded (i.e. considered as false positive) compared to
Allergen Clinical diagnosis SPT
Cat 84% 66%
Mould 79% 58%

Diagnostic test Sensitivity % Specificity % PPV % NPV %
Skin Prick Test >95 30-60 <50 >95
CAP-RAST 57 100 100 36
(If >15kU/L)
Food Challenge ~100 ~100 ~100 ~100

Food-specific IgE level (measured by ImmunoCAP-specific IgE blood test) and probability of reacting to that food after challenge

Predicted relationship between skin prick test result and challenge for peanuts.





SPT with raw peanut extract superior to commercial extract
If SPT to raw extract <3mm: 100% certainty child is not allergic to peanut
If SPT to raw extract >3mm: 74% certainty of allergy
However, if raw extract > 16mm: 100% certainty of peanut allergy
If ImmunoCAP > 57KU (A) / L = 100% positive

 predictive value
DBPCFC can be avoided if:
– SPT to raw extract <3mm and ImmunoCAP <57
KU/L and also when
– SPT to raw extract >16mmm or CAP > 57 KU/L
JACI Vol 109, 6,June 2002, Pg 1027-33

Skin tests
 Prick: Reproducible, sensitive, not irritant
 Prick-prick: Use raw or cooked food. Highly recommended for fruits and vegetables (commercially prepared extracts are generally inadequate because of the lability of the allergens, so the fresh food must be used for skin testing)
 CAP-RAST: Good for follow-up for out-grown allergy.
 Patch test: Atopic dermatitis, delayed reactions, fresh food is recommended

Patients referred for peanut or tree nut allergy

A, Tree nut allergy and sensitization rates in patients with peanut allergy (n 5 234). B, Tree nut allergy rates in relation to peanut allergy for patients with tree nut allergy (n 5 128). TN, Tree nut.
Peanut
Tree Nut







Benzyl Pennicillin
Penicillin Polylysine (major determinant)
Minor determinant mixture
Amoxycillin
Augmentin
Flucloxacillin



In USA study: 566 history positive pts with negative SPT received penicillin:
– 1.2% had possible IgE rxn
– None of the 568 history negative and SPT negative pts had any rxn
– Of the 167 SPT positives, 9 received penicillin and only 2 had IgE-compatible rxn
Conclusion: Skin testing for penicillin is sensitive but not very specific



Review by Weiss & Adkinson in 1988:
– In pts with positive history & positive SPT only a
50 – 70% risk of drug rxn
– Benzylpennicilloyl –specific IgE detetcted in 60-
95% of pts with positive SPT to peniilloylpolylysine
1983-90, 175 pts referred by GPS to allergy clinic, with h/o immediate rxn to penicillin.
– 132 tested & 4 had positive ImmunoCap RAST
– The 128 that tested negative challenged with oral penicillin and none reacted
– So, Clinical sensitivity is good


Specificity of CAP RAST to Pen G, Pen
V, Ampicillin and amoxil was 89% when compared to negative SPT in
105 pts with positive history

300 children with suspected penicillin allergy evaluated in OPD:
SPT with Benzylpennicilloyl-polylysine (Major determinant) & Minor determinant mixture
(MDM)
RAST performed with Benzylpennicilloyl and phenoxymethylpenicilloyl conjugated on disc
Procedure Children with positive results
Skin Tests 48 (16) *
– Major determinant 30
– Minor determinant 11
– Both 7
RAST 42 (14)
SPT & RAST 33 (11)
Skin Test only 15 (5) 57 (19)
RAST only 9 (3)
*% of total number of children

Relationship of positive penicillin test to time elapsed since adverse reaction
Time interval (months) % with pos results
1 – 3 18.6
4 – 12 9.3
13 – 60 4.5
> 60 1.9
Archives of Childhood Disease, 1980, 55, 857-860

Duration of Rx with Pen % with positive results
Before rxn (hrs)
_______________________________________________
<12 21.2
13 – 24 11.9
25 – 48 6.3
49 – 72 2.1
>72 1.9
Archives of Childhood Disease, 1980, 55, 857-860

Manifestation % with positive results
Accelerated skin rash* 25
Delayed skin rash** 5.6
Urticaria 36.7
Angioedema 54.4
Serum Sickness 100
Anaphylaxis 100
*Skin rash appearing within 24 hrs of Rx
** Skin rash observed >24hrs after starting pen






Prednisolone
Triamcinaline
Methylprednisolone
Hydrocortisone
Dexamethasone








Cefaclor
Insulin (Bovine, human, Porcine)
Isocyanate (painters)
Local Anaesthetic
General Anaesthetic
Gelatin (vaccine rxn)
(Venoms intradermal testing)

Recommended interpretation of food allergen-specific IgE levels (kU/L) in the diagnosis of food allergy
Reactive if > (no challenge needed)
Egg Milk Peanut Fish Soy Wheat
7 15 14 20 65 80
Possible reactive ( MD challenge*) (values between)
Unlikely reactive If < (home challenge ) 0.35 0.35 0.35 0.35 0.35 0.35

Uses of skin prick tests (SPT) and radioallergosorbent testing (RAST)
Things SPT/RAST can tell us

That a patient is sensitised to an allergen


The likelihood of reacting after a food challenge
(restricted range of foods)
That a patient is not sensitised to an allergen and therefore an IgE-mediated reaction to that allergen is very unlikely
Things SPT/RAST cannot tell us


The severity of a reaction if a sensitised patient were exposed
Whether the patient’s symptoms are caused by the allergen

The increased levels of tryptase can normally be detected up to three to six hours after the anaphylactic reaction.

Levels return to normal within 12 - 14 hours after release
Normal <11.4


Double -blind

Single-Blind

Open

Double-blind placebo controlled (DBPCFC)

Exercise + oral challenge

Inhalation challenge






Atypical Eczema & non-immediate skin reactions
Allergic Contact Dermatitis
Occupational asthma & dermatitis
Drug Reactions, especially delayed
Non-immediate Food Reactions

Technique PPA NPA
SPT (early reaction) 9% 95%
SPT (late-phase reaction) 41% 81%
APT 81% 93%
NPA = Negative predictive accuracy
PPA = Positive predictive accuracy
Niggemann et al, Allergy 2000;
55::281-285

Food Protein-Induced Enterocolitis
Syndrome (F Pies)





Profuse vomiting & diarrhea-> dehydrated
Presents in 1 st weeks or months or later in exclusively breast fed child upon introducing solids or formulae
Often misdiagnosed as “tummy bug”
Triggers:
– Cow’s milk, soy
– Oats, rice, Barley
Diagnosis:
– Negative SPT & RAST
– Atopy Patch Test: milk, soy, oats, wheat, barley, rice







Presents as reflux
Poor response to omeprazole
Atopic
Diagnosed with:
– SPT, RAST & APT
– Biopsy of esophagus: High eosinophils >15/hpv
Triggers:
– milk, eggs, peanuts, shellfish, peas, beef, chicken, fish, rye, corn, soy, potatoes, oats, tomatoes and wheat
Rx: Swallowed Fluticasone







IgG antibody tests (Great Smokies lab)
Applied kinesiology (Muscle Testing)
Hair analysis
Electrodermal Tests (Vega Testing)
Iridology
Cytotoxic Test (Changes in WBC)