Component-resolved diagnostics (CRD), how to read the result

Maps the commonly ordered allergen components onto their protein family, their stability to heat and digestion, and what a positive result actually predicts. Stable families (storage proteins, lipid transfer proteins) carry systemic-reaction risk; labile families (PR-10, profilin) usually mean oral symptoms only.

Evidence tier: Guideline-derived.

Component	Protein family & stability	What a positive result means
Ara h 2 and Ara h 6 (peanut)	2S albumin storage protein. Stable to heat and digestion.	The most useful single serologic marker for genuine peanut allergy. Positivity predicts systemic reaction risk far better than whole peanut sIgE, which is frequently positive on cross-reactivity alone. Ara h 6 tracks closely with Ara h 2. Ara h 1 and Ara h 3 (7S/11S globulins) are also storage proteins and carry the same implication when positive.
Ara h 8 (peanut)	PR-10 / Bet v 1 homologue. Destroyed by heat and digestion.	Usually reflects birch pollen cross-reactivity rather than true peanut allergy. The typical clinical picture is oral allergy syndrome with raw peanut and tolerance of roasted. An ISOLATED Ara h 8 positive with negative storage proteins argues against systemic peanut allergy, this is the single most common CRD pattern that prevents an unnecessary lifelong avoidance label.
Cor a 14 (hazelnut), Jug r 1 (walnut), Ana o 3 (cashew), Ses i 1 (sesame), Gly m 8 (soy)	2S albumin storage proteins. Stable.	The tree-nut, sesame and soy analogues of Ara h 2. A positive result supports genuine, potentially systemic allergy to that food. Cor a 1 and Cor a 2 (hazelnut PR-10 and profilin) carry the opposite implication and usually indicate pollen cross-reactivity.
Pru p 3 (peach) and its homologues, Ara h 9, Cor a 8, Jug r 3, Tri a 14	Non-specific lipid transfer protein (nsLTP). Stable to heat, digestion and processing.	Systemic-reaction risk, and the dominant food-allergy pattern in Mediterranean populations where it often eclipses pollen-driven allergy. LTP reactions are frequently COFACTOR-dependent (exercise, NSAIDs, alcohol), so a patient can tolerate the food at rest and react to the same food with a cofactor, do not clear them on a resting challenge alone.
Bet v 1 homologues, Mal d 1 (apple), Pru p 1 (peach), Cor a 1 (hazelnut), Gly m 4 (soy)	PR-10. Labile to heat and digestion.	Birch-pollen-driven cross-reactivity: oral itch and tingling with the raw food, usually tolerated cooked. IMPORTANT EXCEPTION: Gly m 4 can cause systemic reactions, particularly to soy beverages and soy protein supplements, so a positive Gly m 4 should not be dismissed as merely oral.
Profilins, Bet v 2, Ara h 5, Cor a 2, Pru p 4	Profilin. Highly labile; pan-allergen across pollens, fruits and vegetables.	Usually clinically irrelevant on its own. Its main practical role is explaining widespread, confusing multi-food sIgE positivity in a patient who eats those foods without difficulty. Treat as cross-reactivity noise unless the history genuinely fits.
Tri a 19 (omega-5 gliadin, wheat)	Gliadin storage protein. Stable.	The marker for wheat-dependent exercise-induced anaphylaxis. Routine wheat SPT and whole-wheat sIgE are frequently NEGATIVE in WDEIA, so this component is what makes the diagnosis in a patient who reacts to wheat only alongside exercise, NSAIDs or alcohol.
Gal d 1 (ovomucoid) vs Gal d 2 (ovalbumin), egg	Gal d 1 is heat-stable; Gal d 2 is heat-labile.	The baked-egg question. Gal d 1 positivity predicts reaction to BAKED egg and a more persistent allergy; a low or negative Gal d 1 with positive Gal d 2 raises the possibility of baked-egg tolerance. It informs, but does not replace, a supervised baked-egg challenge.
Bos d 8 (casein) vs Bos d 4 / Bos d 5 (whey), milk	Casein is heat-stable; alpha-lactalbumin and beta-lactoglobulin are more labile.	The baked-milk counterpart. High casein predicts reaction to baked milk and a more persistent course; whey-predominant sensitisation is more compatible with baked-milk tolerance. Again informative, not a substitute for a supervised challenge.
Alpha-gal (galactose-alpha-1,3-galactose)	Oligosaccharide, not a protein. Present in non-primate mammalian tissue.	Delayed (typically 3-6 hour) reactions to mammalian meat after tick bite sensitisation, and immediate reactions to cetuximab. The delay and the absence of a mealtime-proximate trigger are why this is missed; suspect it in adult-onset "idiopathic" anaphylaxis.
CCD, cross-reactive carbohydrate determinants (e.g. MUXF3)	Carbohydrate epitope shared across plant and insect glycoproteins.	Clinically IRRELEVANT in almost all cases, but a common cause of false-positive extract-based sIgE across many unrelated plant foods and venoms. A CCD-positive patient with broad, clinically silent positivity is the classic reason to move to component testing. Also the reason venom testing can appear dual-positive to both honeybee and vespid.
Api m 1 (honeybee) and Ves v 5 / Ves v 1 (vespid)	Species-specific venom proteins, free of CCD interference.	Used to resolve apparent DUAL positivity to bee and wasp on whole-venom testing, which is usually CCD cross-reactivity rather than true double sensitisation. Identifying the genuine culprit determines which venom immunotherapy the patient receives, a decision with years of treatment behind it.

Notes

CRD does NOT replace the oral food challenge. The challenge remains the diagnostic reference standard; components refine probability and risk, they do not settle the diagnosis.
Order components to answer a QUESTION raised by history and extract testing, most often to resolve discordance or to explain broad positivity. Ordering a component panel as a screen reproduces the same over-diagnosis problem as ordering broad extract panels.
The single most useful organising principle: heat- and digestion-STABLE families (2S albumins and other storage proteins, nsLTP) associate with systemic reactions, while LABILE families (PR-10, profilin) associate with oral symptoms and tolerance of the cooked food.
A negative component does not exclude allergy. Component panels are not exhaustive, sensitisation can be to an untested protein, and assay performance varies by platform.
Sensitisation is not allergy. A positive component in a patient who eats the food without symptoms is not a reason to start avoidance.
Cofactor-dependent presentations (LTP and omega-5 gliadin in particular) can pass a resting oral food challenge. If the history is cofactor-linked, a negative resting challenge does not clear the patient.

Evidence & citations

Clinician decision support. Verify against the cited source. Not a substitute for clinical judgment. 100% on-device; no patient data is stored or transmitted.