Lead
When a doctor says "the IgE for egg came back positive," most parents hear: "no more eggs."
That interpretation is understandable, but not quite accurate. IgE positive means "sensitized" — meaning antibodies to that food are detectable in the blood. But sensitization and "developing symptoms when you eat the food" are not the same thing. Understanding the gap between those two states is what keeps unnecessary food elimination from undermining a child's nutrition and quality of life.
Background: The Gap Between Sensitization and Reaction
When specific IgE: immunoglobulin E, an antibody produced in allergic responses that binds to allergens and triggers mast cell reactions is detected, the condition is called sensitization. Not every sensitized child develops food allergy symptoms — and conversely, some children develop symptoms even without detectable IgE (through non-IgE-mediated pathways).
In HealthNuts, a population-based Australian study of about 2,800 one-year-olds, 16.5% were sensitized to raw egg white on skin prick testing, but only 8.9% had raw egg allergy confirmed by oral food challenge [1]. Flipped around: roughly half of the sensitized infants could eat egg without a reaction. The rule "IgE positive → remove from diet" would unnecessarily eliminate food from a meaningful proportion of children.
The European Academy of Allergy and Clinical Immunology (EAACI) guidelines recommend against ordering food elimination based on IgE levels alone, and instead call for correlation with clinical symptoms and confirmation via Oral Food Challenge (OFC) [2].
The ImmunoCAP Class System — Higher Numbers Do Not Mean "Will React"
Specific IgE testing (ImmunoCAP: a blood test that quantifies specific IgE antibodies to individual allergens, reported in standardized classes from 0 to 6) is reported in classes from 0 to 6.
- Class 0: < 0.35 UA/mL (negative)
- Class 1: 0.35–0.69 UA/mL
- Class 2: 0.70–3.49 UA/mL
- Class 3: 3.5–17.4 UA/mL
- Class 4: 17.5–49.9 UA/mL
- Class 5: 50–99.9 UA/mL
- Class 6: ≥ 100 UA/mL
Higher classes correlate statistically with higher probability of reaction. But predictive power at the individual level has real limits.
A 2015 systematic review by Calvani et al. (37 studies) concluded that specific IgE and skin prick tests for egg have good sensitivity: the proportion of truly allergic children the test correctly flags as positive but low specificity: the proportion of truly non-allergic children the test correctly flags as negative — many "positive" children can in fact eat egg [3]. The same review also lists age-specific values above which raw egg allergy seems very likely even without a challenge: egg-white IgE ≥ 1.7 UA/mL (class 2) under age 2, and ≥ 7.3 UA/mL (class 3) from age 2 [3]. But such cutoffs vary widely between studies and populations and may not transfer to another child [7]. In other words, the class number alone can neither rule egg out nor clear it; it has to be read together with age, the food, and symptom history, and that judgment belongs to the doctor.
The food allergy practice guidelines published by the Japanese Society of Pediatric Allergy and Clinical Immunology (2021 edition) similarly recommend against elimination based on IgE values alone [4].
Oral Food Challenge — The Gold Standard for Definitive Diagnosis
An OFC: Oral Food Challenge, a supervised procedure in which a food is given in incrementally increasing amounts to determine whether a clinical reaction occurs (Oral Food Challenge) is the most reliable method currently available for assessing "whether this child, today, will react to this food." It directly measures what IgE levels cannot: the child's actual threshold at a given point in time [2,4].
An OFC involves administering gradually increasing amounts of the food under observation. Both inpatient and outpatient protocols exist; the choice depends on assessed risk. In Japan, the "Oral Food Challenge Guide 2020," compiled by a Ministry of Health, Labour and Welfare research group and announced by the Japanese Society of Pediatric Allergy and Clinical Immunology, sets out indications, risk assessment, procedures, and how to interpret results [5].
Once a threshold is established by OFC, management becomes concrete: is complete elimination needed, or is a small amount tolerable? That answer changes daily life considerably.
It also matters that many food allergies in early childhood resolve over time. In an Australian population-based cohort, 47% of infants with challenge-confirmed egg allergy at age 1 had outgrown it by age 2 [6]. This makes periodic reassessment — re-testing IgE levels combined with an OFC plan — an important part of ongoing care [4].
The Risks of Unnecessary Elimination
Continuing a food elimination may feel like the cautious choice, but it carries its own risks. Egg, cow's milk, and wheat are present across a wide range of foods; prolonged elimination of all three carries nutritional consequences that should not be dismissed. And in the LEAP trial (Du Toit et al., 2015), which enrolled 640 infants at high risk of peanut allergy, those who ate peanut regularly from infancy — after a doctor's assessment — had far less peanut allergy at age 5 than those who avoided it (1.9% vs 13.7% among infants with a negative skin test at the start) [8]. For egg, infants who tolerated baked egg and ate it frequently were more likely to outgrow their allergy [6]. Not eating a food is not automatically the safe side.
"Confirming the rationale for this elimination with the doctor" is the first practical step against over-restriction.
Putting It Into Practice
1. Do not eliminate a food based on IgE positivity alone. Ask your doctor whether an OFC is appropriate. Whether elimination is warranted, or whether a threshold evaluation via OFC is the next step, cannot be determined from a blood test alone.
2. If elimination is necessary, establish the threshold clearly — complete elimination or is a small amount acceptable? Managing to a doctor-defined threshold, rather than "cut out everything to be safe," has a direct effect on the child's quality of daily life.
3. Recheck IgE every one to two years to track tolerance development. Food allergies in early childhood change. Continuing to manage based solely on older results is a risk in itself.
Keeping a record of symptoms — when, what was eaten, what symptoms appeared — makes accurate evaluation easier when you see the doctor. Mild reactions in particular tend not to stick in memory; written records improve diagnostic precision.
Summary
IgE positive is sensitization, not diagnosis. A high class is a statement about probability, not an individual prediction. An Oral Food Challenge is the most reliable way currently available to determine how much, if anything, this child can eat today.
Elimination is easy to start and hard to stop. To prevent years of groundless restriction, asking the doctor "what is the basis for this elimination?" is what keeps a child's dietary possibilities open.
References
- Osborne NJ, Koplin JJ, Martin PE, et al; HealthNuts Investigators. Prevalence of challenge-proven IgE-mediated food allergy using population-based sampling and predetermined challenge criteria in infants. J Allergy Clin Immunol. 2011;127(3):668–676. PMID: 21377036.
- Muraro A, Werfel T, Hoffmann-Sommergruber K, et al; EAACI Food Allergy and Anaphylaxis Guidelines Group. EAACI food allergy and anaphylaxis guidelines: diagnosis and management of food allergy. Allergy. 2014;69(8):1008–1025. PMID: 24909706.
- Calvani M, Arasi S, Bianchi A, et al. Is it possible to make a diagnosis of raw, heated, and baked egg allergy in children using cutoffs? A systematic review. Pediatr Allergy Immunol. 2015;26(6):509–521. PMID: 26102461.
- Japanese Society of Pediatric Allergy and Clinical Immunology, Food Allergy Committee. Food Allergy Practice Guidelines 2021. Kyowa Kikaku; 2021.
- Ministry of Health, Labour and Welfare research group on standardizing oral food challenges (principal investigator: Ebisawa M). Oral Food Challenge Guide 2020 [食物経口負荷試験の手引き2020]. Released March 2021.
- Peters RL, Dharmage SC, Gurrin LC, et al; HealthNuts study. The natural history and clinical predictors of egg allergy in the first 2 years of life: a prospective, population-based cohort study. J Allergy Clin Immunol. 2014;133(2):485–491. PMID: 24373356.
- Peters RL, Gurrin LC, Allen KJ. The predictive value of skin prick testing for challenge-proven food allergy: a systematic review. Pediatr Allergy Immunol. 2012;23(4):347–352. PMID: 22136629.
- Du Toit G, Roberts G, Sayre PH, et al; LEAP Study Team. Randomized trial of peanut consumption in infants at risk for peanut allergy. N Engl J Med. 2015;372(9):803–813. PMID: 25705822.