Presentation is loading. Please wait.

Presentation is loading. Please wait.

GP CME Allergy Diagnosis Workshop Waipuna Conference Center Friday 13 August 2010 Vincent St Aubyn Crump.

Similar presentations


Presentation on theme: "GP CME Allergy Diagnosis Workshop Waipuna Conference Center Friday 13 August 2010 Vincent St Aubyn Crump."— Presentation transcript:

1 GP CME Allergy Diagnosis Workshop Waipuna Conference Center Friday 13 August 2010 Vincent St Aubyn Crump

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

3 Clinical Assessment 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

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

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

6 Likelihood Ratio (LR) 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. 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 positive = sensitivity / (1 - specificity) LR negative = (1 - sensitivity) / specificity LR negative = (1 - sensitivity) / specificity LR is better than sensitivity & specificity because it is less likely to change with prevalence of disorder LR is better than sensitivity & specificity because it is less likely to change with prevalence of disorder

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

8 Total IgE Total IgE – Normal Reference Interval Age (years) Range (IU/ml) < – – 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 non- specific binding of IgE antibodies Very high levels of total IgE can give false positive Specific IgE results (multiple allergens tested positive), due to non- specific binding of IgE antibodies

9 Disease indications for skin prick testing To confirm atopy, assisting in the diagnosis of asthma, eczema in infants To confirm atopy, assisting in the diagnosis of asthma, eczema in infants –Especially differentiating transient wheezers in infancy from persistent / asthmatics Before initiating immunotherapy Before initiating immunotherapy To monitor progress during immunotherapy To monitor progress during immunotherapy Acute Urticaria & Anaphylaxis Acute Urticaria & Anaphylaxis All asthmatics requiring therapy All asthmatics requiring therapy Occupational Diseases including latex allergy Occupational Diseases including latex allergy Eczema 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. 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 Stinging insect anaphylaxis Rhinitis vs Sinusitis Rhinitis vs Sinusitis

10  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) Diagnosing IgE-mediated food: Skin Prick Test

11  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 IgE- mediated food allergy Diagnosing IgE-mediated food hypersensitivity disorders with ImmunoCAP

12 Comparison of in-vivo (SPT) with in-vitro Immuno CAP-RAST Feature Importance SPT CAP-RAST Availability Speed of results Sensitivity Specificity Standardization Quantification of results Temp. Stability Reagent stability Drugs effects Educational

13 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 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 In presence of dermographism Patient unable of unwilling to stop medications like antihistamines and some antidepressants Patient unable of unwilling to stop medications like antihistamines and some antidepressants Allergy to fruits & Vegetables. Do prick-prick test instead Allergy to fruits & Vegetables. Do prick-prick test instead Within 6 weeks of an anaphylactic reaction. Within 6 weeks of an anaphylactic reaction. If therapy for anaphylaxis is not readily available If therapy for anaphylaxis is not readily available Extreme caution in pregnancy Extreme caution in pregnancy

14 Drugs affecting Skin Prick Test Drug Degree of supression Duration of supression Loratidine ++ 3 – 5 days Cetirizine days Phenergan – 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

15 Practice name / Ordering physician: Practice name / Ordering physician: Street address City Telephone Fax Street address City Telephone Fax Patient name: ______________________________ Date of birth: __/__/__ Patient name: ______________________________ Date of birth: __/__/__ Testing Technician: _______________________ Testing Technician: _______________________ Last use of antihistamine (or other med affecting response to histamine): ___ days Last use of antihistamine (or other med affecting response to histamine): ___ days medication __________________ medication __________________ Testing Date (s) and Time: Percutaneous __/__/_____________AM PM Testing Date (s) and Time: Percutaneous __/__/_____________AM PM Intradermal __/__/_____________AM PM Intradermal __/__/_____________AM PM General information about skin test protocol 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, * 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 House dust mites Milk Cat Egg Cat Egg Dog Wheat Dog Wheat Skin Prick Test Form

16 Interpretation of Test Results The wheal & flare should be recorded in millimeters The wheal & flare should be recorded in millimeters 3 mm is considered the cut-off for positive, but may overestimate clinical allergy! 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 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 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!) 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 In hyperpigmented skin the indurations might have to be palpated Remember that sensitivity (positive skin prick tests) does not mean clinical reactivity or allergy. Remember that sensitivity (positive skin prick tests) does not mean clinical reactivity or allergy.

17 Size of SPT wheal (mm) 100% likelihood of + Challenge Milk Egg Peanut 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: )

18 Comparison of Skin Test (>3mm) vs. DBPCFC NPV PPV NPV PPV Food High Risk Low Risk High Risk Low Risk Egg 90 % 99%85%17% Milk90%99%66%2% Peanut75%99%55%15% Soy84%97%35%12% Wheat94%98%35%15% Fish80%99%77%30%

19 History of RAST RAST (radioallergosorbent test) invented and marketed in 1974 RAST (radioallergosorbent test) invented and marketed in 1974 The suspected allergen is bound to an insoluble material and the patient's serum is added 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 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 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 unbound anti-human IgE antibodies are washed away. The amount of radioactivity is proportional to the serum IgE for the allergen The amount of radioactivity is proportional to the serum IgE for the allergen

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

21 ImmunoCAP (RAST)

22 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 (child) >7 Egg (age 2 Egg (age 2 Cow’s milk (child) >15 Cow’s milk (child) >15 Cow’s milk (age 5 Cow’s milk (age 5 Peanut >14 Peanut >14 Fish >20 Fish >20

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

24 Performance characteristics of diagnostic tests for peanut allergy Diagnostic test Sensitivity % Specificity % PPV % NPV % Skin Prick Test > CAP-RAST (If >15kU/L) Food Challenge ~100 ~100 ~100 ~100

25 Specific IgE level related to the probability of a food reaction Food-specific IgE level (measured by ImmunoCAP-specific IgE blood test) and probability of reacting to that food after challenge

26 Predicted relationship between specific IgE and challenge for peanuts

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

28 Improved screening for peanut allergy by combining SPT to raw peanut & ImmunoCAP SPT with raw peanut extract superior to commercial extract 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: 100% certainty child is not allergic to peanut If SPT to raw extract >3mm: 74% certainty of allergy If SPT to raw extract >3mm: 74% certainty of allergy However, if raw extract > 16mm: 100% certainty of peanut allergy However, if raw extract > 16mm: 100% certainty of peanut allergy If ImmunoCAP > 57KU (A) / L = 100% positive predictive value If ImmunoCAP > 57KU (A) / L = 100% positive predictive value DBPCFC can be avoided if: 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

29  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 Diagnosing food hypersensitivity disorders: Summary Skin tests

30 ImmunoCAP RAST for diagnosis of peanut, tree nut & seed allergy Patients referred for peanut or tree nut allergy

31 Organ system involvement with peanut, tree nut, and seed reactions.

32 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

33 Penicillin Skin Prick Test & Intradermal testing Benzyl Pennicillin Benzyl Pennicillin Penicillin Polylysine (major determinant) Penicillin Polylysine (major determinant) Minor determinant mixture Minor determinant mixture Amoxycillin Amoxycillin Augmentin Augmentin Flucloxacillin Flucloxacillin

34 Skin Testing in suspected penicillin allergy In USA study: 566 history positive pts with negative SPT received penicillin: 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 Conclusion: Skin testing for penicillin is sensitive but not very specific

35 Penicillin skin testing contd. Review by Weiss & Adkinson in 1988: 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 % of pts with positive SPT to peniilloylpolylysine , 175 pts referred by GPS to allergy clinic, with h/o immediate rxn to penicillin , 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

36 Immuno CAP vs SPT to penicillin 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 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

37 Penicillin allergy: Incidence of positive SPT & ImmunoCAP 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

38 Relationship of positive penicillin test to time elapsed since adverse reaction Time interval (months) % with pos results 1 – – – > Archives of Childhood Disease, 1980, 55,

39 Relationship of positive result to speed of adverse reaction Duration of Rx with Pen % with positive results Before rxn (hrs) _______________________________________________ < – – – > Archives of Childhood Disease, 1980, 55,

40 Relationship of positive results to the type of adverse rxn 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

41 Steroid Testing: Skin Prick & I/D (or Patch Test) Prednisolone Prednisolone Triamcinaline Triamcinaline Methylprednisolone Methylprednisolone Hydrocortisone Hydrocortisone Dexamethasone Dexamethasone

42 Other Drug Tested (ImmunoCAP & skin testing) Cefaclor Cefaclor Insulin (Bovine, human, Porcine) Insulin (Bovine, human, Porcine) Isocyanate (painters) Isocyanate (painters) Local Anaesthetic Local Anaesthetic General Anaesthetic General Anaesthetic Gelatin (vaccine rxn) Gelatin (vaccine rxn) (Venoms intradermal testing) (Venoms intradermal testing)

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

44 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

45 Mast cell Tryptase Normal <11.4 The increased levels of tryptase can normally be detected up to three to six hours after the anaphylactic reaction. Levels return to normal within hours after release

46 Types of challenge testing Double -blind Double -blind Single-Blind Single-Blind Open Open Double-blind placebo controlled (DBPCFC) Double-blind placebo controlled (DBPCFC) Exercise + oral challenge Exercise + oral challenge Inhalation challenge Inhalation challenge

47 Indications for Patch Test Atypical Eczema & non-immediate skin reactions Atypical Eczema & non-immediate skin reactions Allergic Contact Dermatitis Allergic Contact Dermatitis Occupational asthma & dermatitis Occupational asthma & dermatitis Drug Reactions, especially delayed Drug Reactions, especially delayed Non-immediate Food Reactions Non-immediate Food Reactions

48 Predictive values of SPT & APT vs DBPCFC in patients with AD Technique PPA NPA SPT (early reaction) 9% 95% SPT (late-phase reaction) 41% 81% APT 81% 93% NPA = Negative predictive accuracy NPA = Negative predictive accuracy PPA = Positive predictive accuracy PPA = Positive predictive accuracy Niggemann et al, Allergy 2000; 55::

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

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

51 Unproven (useless) Tests widely available in NZ IgG antibody tests (Great Smokies lab) IgG antibody tests (Great Smokies lab) Applied kinesiology (Muscle Testing) Applied kinesiology (Muscle Testing) Hair analysis Hair analysis Electrodermal Tests (Vega Testing) Electrodermal Tests (Vega Testing) Iridology Iridology Cytotoxic Test (Changes in WBC) Cytotoxic Test (Changes in WBC)


Download ppt "GP CME Allergy Diagnosis Workshop Waipuna Conference Center Friday 13 August 2010 Vincent St Aubyn Crump."

Similar presentations


Ads by Google