Skin or In Vitro Test for Food Allergy?
Skin Test
Linda Cox, FAAAI, FACAAI
WAO 2011 Meeting
Cancun, Mexico
Linda Cox, MD Disclosure
Allergist/Immunologist: solo private practice
Associate Clinical Professor of Medicine Nova Southeastern
University
Medical advisory board/consultant: Stallergenes,
Genentech/Novartis, ISTA
Speakers fee: Thermo Fisher, Baxter
Organizational interests:
• FDA Allergenic Products Advisory Committee –consultant
• AAAAI-Secretary/Treasurer
• Joint Task Force on Practice Parameters-member
• ABAI Board of Directors -member
Skin or In Vitro Test for Food Allergy
Learning Objectives
• To recognize that, in general, allergy skin tests
are the preferred tests for food allergy diagnosis
for several reasons
• Be able to discuss scenarios in which skin test
may be superior to serum specific-IgE
Significance Of Positive Allergy Skin Test Results
Food Allergy Diagnostic Testing
Pearls, Pitfalls and the Gold Standard
• Allergy tests yield information on sensitization, which is
not always equivalent to clinical allergy.
• Neither skin or serum sIgE have 100% sensitivity or
specificity
• The double-blind, placebo-controlled food challenge is
the gold standard for food allergies but it is
– a time-consuming procedure that is
– limited to trained allergy specialists and
– carries the risk of producing a severe reaction
4
Probability of a reaction (%)
Food-specific IgE Antibody Concentrations or Skin
Test Size Correlate with Risk of Clinical Reactivity
Curve varies by:
•Food
•Disease
•Age
•Assay (brand)
100
80
60
40
20
0
Food-specific IgE Antibody Concentration (or
Skin Test Wheal Size)
Negative test is not zero risk
Sampson HA.. J Allergy Clin Immunol 2001;107:891-6.
At certain high IgE values,
the chance of a clinical
reaction approaches
certainty
One study, one test
brand,
children age 5: Egg- 7
kUa/L
Milk 15 kIU/L, Peanut 14
kUa/L
50% and 95% Predictive Value have been Established
for Food Specific-IgE and SPT
Food specific-IgE measured with ImmunoCap™ and SPT with lancet (ref 17 & 21,) and
bifurcated needle (ref 22)
Nowak-WÄ et al, Work Group report: Oral food challenge testing. J Allergy Clin Immunol 2009;
123:S365-S83.
Specificity of SPT in predicting positive open food
challenges to milk, egg and peanut in children
• Study: 555 challenges were undertaken in 467 children with
suspected food allergy. Positive challenge if objective signs
seen; negative, if the child could tolerate normal food daily, for
1 week.
• Results: 55% were positive, 37% negative, and 8% inconclusive.
– Possible to identify a SPT wheal at, and above, which
negative reactions did not occur (100% specificity ):
• cow milk, 8mm
• egg, 7mm
• peanut, 8mm
• However positive reactions could occur with a SPT of 0 mm.
Sporik et al, Clin Exp Allergy. 2000;30(11):1540-6.
Positive open food challenges to milk, egg and peanut
in children could occur with 0 mm SPT
MILK
Sporik et al, Clin Exp Allergy. 2000;30(11):1540-6.
PEANUT
Diagnostic accuracy of skin prick testing in
children with tree nut allergy
Study: 906 tree nut and peanut challenges in 680 child aged
4 month to 19 years
Results :
• 8 mm SPT weal diameters >95% accuracy in predicting a
positive OFC for cashew, hazel nut, walnut, and sesame.
• Using the predictive SPT decision points, the need for OFC
was reduced by 33% (peanut), 56% (tree nuts), and 53%
(sesame),
• Not able to determine the 95% PPV for almond, pistachio,
pecan, and brazilnut
Ho et al J Allergy Clin Immunol 2006;117:1506-8
The predictive value of the skin prick test weal
size for the outcome of oral food challenges.
• Study: 735 OFC in 385 children (median
age 22 months), with cow's milk, hen's
egg, wheat and soy.
• Results: 312 (43%) OFC were assessed to
be positive.
– 95% and 99% predicted probabilities
using logistic regression revealed
predictive decision points of:
• 13.0 and 17.8 mm for HE
• 12.5 and 17.3 mm for CM
Verstege et al. Clin Exp Allergy. 2005;35(9):1220-6.
SPT Wheal Size May Useful in Predicting Presence of
Absence of Clinical Allergy
• Study : Challenged 47 peanut-naïve children who had a positive
SPT to peanut (smallpox needle)
• Results: 49% of challenges were positive
• Mean wheal: negative group 6.3 mm vs. positive group 10.3 mm
• Using the cutoff of a > 5 mm wheal on PST, peanut challenge
yielded
– Sensitivity was 100% (no false -)
– Specificity was 12.5% (high false+)
– Negative predictive value was 100%
– Positive predictive value was 52%.
• Conclusion: These findings suggest peanut PST of 3 or 4 mm could
undergo less resource-intensive, accelerated challenges.
Kagan R et al., Ann Allergy Asthma Immunol 2003 Jun;90(6):640-5:
11
Prediction of anaphylaxis during peanut food
challenge: usefulness of peanut SPT & specific IgE
• Study: 89 in-hospital challenges: positive in 56/89
(62.9%) patients:
– In the 55 completed challenges: 28 no rx, 6 reaction
without anaphylaxis, 21 had anaphylaxis
• Mean peanut SPT wheal size and specific IgE level
were associated with the
severity of reactions
on challenge
Wainstein et al . 2010;21(4 Pt 1):603-11
Allergy Skin Testing Advantages
• In the allergist office, skin testing remains the
central test to confirm allergic sensitivity.1
• Advantages:
• Skin testing is fast (15-30 minutes), safe, sensitive and
involves minimally invasive procedures
• Can provide information on allergen sensitivity on initial
clinic visit.
• i.e., no trip to a busy lab for venipuncture
• Cost-effective in terms of patient time & money
• When performed correctly, skin testing is reproducible
1. Oppenheimer et al, Ann Allergy 2006;S1:6-122.
Serological Evaluation for Sensitization to Food
Limitations
– Cost-patient time & money
– Requires venipuncture/or other blood draw
• Modest sensitivity/specificity lead to false positive and
false negative
• Although anyone can order still requires experienced
clinician to optimally interpret data
• Reactions could occur despite a “negative” test
– Several studies show reaction rates over 20% in patients
with “undetectable” food specific serum IgE (with
suspected allergy by history)
– Different Lab assay systems are not interchangeable
Adapted from : the Pearls & Pitfalls of Allergy Diagnostic Testing CME presentation at
www.aaaai.org
Serum specific-IgE Antibody Laboratory Results
Interassay Variability
 Objective: compare results from CLIA-certified
laboratories that used 3 common systems for sIgE
antibody
 Methods: 60 samples for peanut and 20 for soy and
mouse-human chimeric IgE antibodies specific for the Bet
v 1 and Der p 2 were submitted for sIgE measurement on
3 different systems:
 ImmunoCAP, Immulite, and Turbo-RAST
 Reference: total IgE = Chimeric IgE
Wood et al., Annals Allergy, Asthma & Immunol 2007; 99:34-41
15
Poor Agreement of IgE Antibody Laboratory Results
Results: Poor agreement among the 3 systems for soy and peanut
• Using a cutoff of 0.35 kUa/L showed some differences in the ability to
detect sIgE sensitization with Turbo RAST most variable
• Studies suggest various assays measure different populations of IgE
antibody.
• Currently, it is not known which of the major assays provides the
most accurate evaluation of allergen s-IgE in patients’ serum.
Wood et al, Annals Allergy, Asthma & Immunol 2007; 99:34-41
16
Interassay Variability of IgE Antibody Laboratory
Results
• Results: Chimeric antibodies: Widely disparate results
amongst the 3 assays
• Immunlite considerably overestimated sIgE
• Turbo RAST underestimated sIgE
Immunlite
ImmunoCAP
Tubo RAST
Wood et al.,Annals Allergy, Asthma & Immunol 2007; 99:34-41
Allergy Skin Testing Advantages &
Diagnostic Utility in Comparison to
Specific- IgE Antibody
• SPT may be more sensitive in predicting who will
react on challenge
• In pts with low food sIgE, SPT may have
diagnostic utility
• SPT can identify sensitivity to labile food
proteins
The natural history of peanut allergy
Study: 223 peanut allergic pts 4 to 20 yrs were
evaluated by questionnaire, skin testing, & peanut sIgE
• Reaction-free plus peanut sIgE ≤ 20 kUa/L challenged
• Results: 85 pts underwent DBPC or open challenge
– 48 (21.5%) patients passed challenge (‘outgrew allergy’)
– 37 failed challenge: 8(21%) patients with negative peanut
sIgE , 2 of which also had negative SPT
Skolnick et al,J Allergy Clin Immunol. 2001;107(2):367-74
SPT to egg white provides additional diagnostic utility
to serum egg white-sIgE concentration in children
• Study: Retrospective analysis to determine whether the size of the
SPT to egg white adds diagnostic utility for children with low egg
white–sIgE.
• Results: Egg OFCs passed (n = 29) and failed (n = 45)
– 9 (20%) failed OFCs had undetectable (<0.35 kIU/L) egg white–sIgE
levels with egg SPT from 4.0 to 6.0 mm and egg/histamine SPT
indices from 0.67 to 1.71
– Between failed/passed OFC:
• No difference in age, clinical characteristics, or egg white-sIgE
• Significant differences between both egg white SPT wheal and
egg/histamine SPT wheal index.
– 1 failed had negative SPT & sIgE -urticaria 2 hrs later during
placebo phase
Knight et al, J Allergy Clin Immunol. 2006;117(4):842-7
SPT Is Superior To IgE CAPRAST For The Diagnosis Of
Infantile Food Allergy
• Study: Infants with suspected egg and milk allergy with negative
specific-IgE at the time of first visit
• Results:
– Egg: 72/89 (80%) suspected-HE allergies with negative IgE
CAPRAST, were diagnosed as HE allergy by the elimination and
provocation tests . 39 had positive egg SPT
– Milk: 42/125 (33%) suspected-CM allergy infants with negative
IgE were diagnosed as CM allergy, and 21 (50%) had positive
milk SPT
• Authors’ Conclusions: “SPT seemed to be more useful than EW- or
CM- IgE CAPRAST for the diagnosis of HE or CM allergies in early
infantile period.”
Ebisawa M et al, J Allergy Clin Immunol 2009;123(2):S23.
When commercial extracts are just not good enough
• Study: In 430 children with suspected food allergy-compared results
obtained with SPT using commercial extracts and fresh foods, and
labial and/or oral challenge
• Results: egg, peanut, and cow's milk.
– Cow's milk, wheal larger with commercial extracts(NS)
– Conversely, wheal diameters were significantly larger with other
fresh foods
– SPT positive in 40% of commercial extracts and 81.3% with fresh
foods.
– Concordance with positive challenge & SPT: 58.8% with
commercial extracts and 91.7% with fresh foods.
• Results indicate that fresh foods may be more effective for detecting
the sensitivity to food allergens.
Rance et al, Allergy. 1997;52(10):1031-5.
Diagnosing IgE-mediated hypersensitivity to sesame by
an immediate-reading "contact test" with sesame oil
• 3 cases of immediate reaction to sesame:
– 42-yo man: 2 anaphylactic reactions after ingestion of breadsticks
and candy,
– 28-yo man : 2 urticaria/angioedema reactions within 10 minutes
after ingesting bread containing sesame seeds.
– 38-year-old man several urticaria/angioedema reactions within 30
minutes after ingesting sesame-containing foods
– All 3 with negative SPT to commercial extract and none had
detectable sesame-specific IgE
– SPT to sesame oil and crushed sesame was negative: note
oleosins are hydrophobic and can not be solubilized in saline
Alonzi J Allergy Clin Immunol 2011;127:1627-9
When Commercial Extracts, Prick to Prick & Serum IgE
Antibody Test Fail to Diagnose
The Skin “Contact Test “
• An immediate-reading ‘‘contact test’’ was performed by
applying on the volar side of the forearm a square of filter
paper (10 x 10 mm) dipped in sesame oil and removing it
after 20 minutes.
• Results: Patient 2 had wheal reaction the same size as the
filter paper at contact site, whereas patients 1 and 3 had
several 4-mm wheals also involving the surrounding area
• Immediate-reading contact test with sesame oil was negative
in 10 healthy subjects & 3 pts tolerated other oil contact tests
Alonzi J Allergy Clin Immunol 2011;127:1627-9
Allergy Skin Test vs. In Vitro Tests
What about the side effects, risks and dangers?
28
Reactions to prick and intradermal skin tests
Methods: 12-month prospective study was conducted
to evaluate SRs from ST in 1,456 patients
Results:
• Six patients (0.4%) had SRs during SPT. 1 reacted to
aeroallergens alone, whereas the other 5 reacted to
aeroallergens and food
• No severe asthma, shock, hypotension,
unconsciousness, or biphasic reactions occurred.
• All 52 patients received epinephrine intramuscularly
Bagg A, Chacko T, Lockey R. Ann Allergy Asthma Immunol. 2009;102(5):400-2.
Systemic reactions to allergy skin tests
Method: Retrospective study at the Mayo Clinic to identify patients
who developed systemic reactions to skin tests
Results:. 497,656 skin tests were performed : SPT 16,505 patients
– 6 patients experienced SRs. All had asthma.
– SPT SR rate was 15 or 23 reactions per 100,000 aeroallergen
tests
• “It is noteworthy that there were no systemic reactions to skin tests
for foods or venoms”
• Conclusion: SR to skin tests was very low. SRs were mild and all
patients recovered fully within 1 hour.
Valyasevi et al, Ann Allergy Asthma Immunol 1999;83:132–136.
30
Risk of adverse reactions from SPT, venipuncture, and
body measurements: NHANES II 1976-80
Study: 16,204 of the U.S. population , 6 to 74 yrs, examined with
routine medical procedures, including SPT & venipuncture.
• SPT to 8 FDA licensed unstandardized extracts
Results:
• SPT: No anaphylactic reactions after SPT were observed.
• Venipuncture: One asthmatic reaction. Other AR limited to syncope,
near syncope, and malaise.
• Adverse reaction rates:
– Venipuncture: 0.49% (95% CI, 0.38% to 0.60%);
– SPT: 0.04% (95% CI, 0.01%-0.08%);
– Age group 20 to 49 years had the highest occurrence of any AR to
venipuncture (0.87%; 95% CI, 0.633% to 1.107%).
Turkeltaub J Allergy Clin Immunol. 1989;84(6 Pt 1):886-90
Allergy Skin Testing…moving into the future
Molecular Allergy: Can allergy skin tests meet the challenge?
Scarification Device
Modified-Prick
Puncture
Multiplex Array
• In 1930s, scarification - problem was a lack of uniformity in the abrasion AND
there was the potential side effect of scarring.
• Mueller device made six uniform abrasions 1-½ mm long and 15 mm apart
• Pepys modified prick skin test method in 1968.
• Studies comparing scarification to SPT showed increased false – and +
• As a result, use of the scarification technique diminished in 1970’s
Component-resolved diagnosis of pollen allergy based on
SPT with profilin, polcalcin and LTP pan-allergens
• Principle objective: evaluate a new diagnostic strategy - SPTs
specific for 3 pan-allergens, together with an appropriate and
complete panel of allergenic molecules.
• Study :1329 pts with previous 2-year history of pollinosis, tested by
vitro method to 13 purified allergen including pan-allergens & SPT
to major allergens and pan-allergens
• For SPT:
– peach commercial extract adjusted to 30 mg/mL of Pru p 3,
which is a LTP
– date palm extract: natural profilin, Pho d 2 adjusted to 50
mg/mL & procalin
Component-resolved diagnosis of pollen allergy based on
SPT with profilin, polcalcin and LTP pan-allergens
Concordance of SPT extracts and sIgE to the corresponding
pan-allergens
Results:
• Concordance of SPT extracts and sIgE evaluated: high diagnostic value
is observed for
• Profilin SPT (positive and negative concordance 82.3% and
90.8%, respectively)
• LTP-enriched SPT (positive and negative concordance 65% and
94.3% respectively ),
– Polcalcin SPT performance lower (positive and negative
concordance 50% and 90.4% respectively).
• Authors’ conclusion: “ Novel diagnostic strategy has proven to be a
valuable tool in daily clinical practice. Introduction of routine SPT to
pan-allergens is a simple and feasible way of improving diagnostic
efficacy.”
Barber et al,Clin Exp Allergy 2009;39:1764-73
Why Skin Testing is Superior to In Vivo Testing
Because:
• More cost and time efficient for patient
– Results available on initial consultation allowed for
development of specific treatment plan
• Predictive value in terms of presence of clinical
allergy and possible severity
– In some cases greater predictive value than in vivo
test
• Ability to test to allergens that may be altered in
extract preparation process e.g., natural foods
• Can also be used in component-resolved
diagnosis