Quick Answer
Component-resolved diagnostics (CRD) measures IgE to specific allergen molecule components — individual proteins within an allergen source — rather than to the whole extract. For peanut, IgE to Ara h 2 predicts systemic anaphylaxis risk while IgE to Ara h 8 predicts only mild oral allergy syndrome. CRD enables more precise risk stratification and reduces unnecessary food avoidance.
What Component Testing Measures
Traditional allergy testing measures IgE to a crude extract containing all proteins from the allergen source. For example, 'peanut extract' contains over 17 different proteins (Ara h 1–17). A patient may be positive to the whole extract based on IgE to a single benign protein while lacking IgE to the dangerous proteins that cause anaphylaxis. This can either overestimate or underestimate clinical risk.
Component-resolved diagnostics (CRD) uses the ImmunoCAP ISAC microarray or individual ImmunoCAP assays to measure IgE to purified recombinant or natural individual allergen components. This allows identification of exactly which protein(s) the patient is sensitized to, enabling much more precise risk stratification.
Peanut Component Testing: Ara h 2 vs Ara h 8
The most clinically impactful application of CRD is peanut allergy. Ara h 2 (a 2S albumin, heat-stable) is the major marker of true systemic peanut allergy — high IgE to Ara h 2 predicts a very high probability of reacting with anaphylaxis on peanut challenge. In contrast, Ara h 8 is a PR-10 protein cross-reactive with birch pollen Bet v 1. Patients sensitized only to Ara h 8 typically have only oral allergy syndrome from peanut — mild mouth tingling without systemic risk.
This distinction is clinically critical: a patient with a positive peanut extract result based only on Ara h 8 sensitization may be mistakenly told to carry epinephrine and avoid peanut entirely, when in reality they have only pollen cross-reactivity and can likely eat peanut-containing foods safely. CRD prevents this diagnostic error and its associated quality-of-life impact.
Component Testing for Other Allergens
CRD has expanding clinical utility across multiple allergen categories. For hazelnut allergy, Cor a 14 (2S albumin) predicts systemic allergy while Cor a 1 (PR-10) predicts only birch cross-reactivity and mild OAS. For milk allergy, casein-specific IgE predicts more severe and persistent allergy than whey protein IgE. For tree pollen cross-reactivity across multiple allergens, Bet v 1 (birch) is the primary sensitizer, and other species positivity reflects cross-reactivity rather than independent sensitization.
Cat allergy component testing for Fel d 1 vs Fel d 4 (albumin) is useful because albumin-sensitized patients may react to multiple mammals (cat, dog, horse, pork) through pork-cat syndrome or albumin cross-reactivity — requiring broader avoidance than Fel d 1-only sensitization.
Key Takeaways
- CRD measures IgE to specific allergen proteins rather than whole extracts — enabling molecular-level diagnosis.
- Peanut Ara h 2: predicts anaphylaxis risk. Ara h 8: predicts only birch cross-reactive oral allergy syndrome — no systemic risk.
- CRD prevents misdiagnosis of pollen-food syndrome as true food allergy, reducing unnecessary avoidance.
- Hazelnut Cor a 14 (systemic risk) vs Cor a 1 (OAS only) parallels the peanut Ara h 2 vs Ara h 8 distinction.
- ImmunoCAP ISAC microarray tests 112 allergen molecules simultaneously from a single blood sample.
Related Guide
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