Traditional allergy testing — skin prick testing and specific IgE blood tests — uses whole allergen extracts (e.g. whole peanut extract, whole egg extract). While these tests are useful, they cannot always tell us how severe a child's allergy is likely to be, or whether a positive result represents a true clinical allergy or simply sensitisation.

Component-resolved diagnostics (CRD) — also called molecular allergy testing — goes a step further by testing for specific proteins within an allergen. This gives a more detailed and accurate picture of the allergy, helping to predict reaction severity and guide management decisions.

How Does CRD Work?

Every allergen (peanut, egg, milk, birch pollen, etc.) is made up of multiple different proteins. Some of these proteins are more likely to cause severe reactions than others. CRD tests for IgE antibodies against individual proteins, rather than the whole allergen extract.

For example, peanut contains many different proteins. Two of the most clinically important are:

  • Ara h 2 (a storage protein): High levels of IgE to Ara h 2 are strongly associated with severe, systemic reactions to peanut — including anaphylaxis. A child with high Ara h 2 IgE is at significant risk of a severe reaction if they eat peanut.
  • Ara h 8 (a PR-10 protein, cross-reactive with birch pollen): IgE to Ara h 8 is associated with mild, localised reactions (oral allergy syndrome) rather than systemic reactions. A child sensitised only to Ara h 8 may be able to tolerate roasted peanut.

Without CRD, both children would show a positive peanut IgE result — but their clinical risk is very different. CRD allows Dr Anandarajan to distinguish between them.

When Is CRD Used?

CRD is particularly useful in the following situations:

  • Peanut allergy: To distinguish between high-risk allergy (Ara h 2 positive) and pollen-related sensitisation (Ara h 8 positive), and to guide decisions about whether a food challenge is needed
  • Tree nut allergy: To identify which specific nut proteins are responsible and whether cross-reactivity between nuts is likely
  • Hazelnut allergy: To distinguish between true hazelnut allergy (Cor a 9/14 positive — higher risk) and pollen-related hazelnut sensitisation (Cor a 1 positive — lower risk, oral allergy syndrome)
  • Wheat allergy: To distinguish between wheat allergy and wheat-dependent exercise-induced anaphylaxis (WDEIA), which involves omega-5 gliadin (Tri a 19)
  • Latex allergy: To identify cross-reactive foods (banana, avocado, kiwi)
  • Deciding whether a food challenge is safe: CRD results help predict whether a supervised food challenge is likely to be safe or whether the risk of a severe reaction is too high

How Is CRD Performed?

CRD is performed as a blood test. A small blood sample is taken and sent to the laboratory for analysis. Results are typically available within a few days. Dr Anandarajan will discuss the results at a follow-up appointment and explain what they mean for your child's management.

CRD can also be performed using a multiplex platform (ImmunoCAP ISAC or Alex2), which tests for IgE against over 100 different allergen components from a single small blood sample. This is particularly useful for children with multiple allergies or complex allergy profiles.

CRD and the Food Challenge Decision

One of the most important uses of CRD is in deciding whether a supervised food challenge is appropriate. A food challenge involves giving a child increasing amounts of the allergenic food under medical supervision to determine whether they are truly allergic or whether they can tolerate it.

CRD results — particularly Ara h 2 levels for peanut — help predict the likely outcome of a food challenge and whether the risk of a severe reaction is acceptable. Children with very high Ara h 2 levels may be advised to avoid a food challenge due to the risk of anaphylaxis.

Is CRD Available at Belfast Children's Allergy Clinic?

Yes. Dr Anandarajan offers component-resolved diagnostics as part of the comprehensive allergy assessment at Belfast Children's Allergy Clinic. CRD is available for peanut, tree nuts, egg, milk, wheat, sesame and other allergens.

Read more about skin prick testing and what happens during allergy testing.

Book an Appointment

To discuss whether CRD is appropriate for your child, call 028 9066 7878 or book online at kph.fyi/Book-MAnandarajan. No GP referral is required.