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Molecular allergology · Patient guide

ISAC test, the multi-allergen chip that measures IgE to 112 molecular allergen components.

The ISAC test (ImmunoCAP ISAC) is a multiplex allergy blood test that measures specific IgE against 112 allergen components on a single chip. Modern molecular allergology in cases of complex or multiple allergies, unexplained anaphylaxis and cross-reactivity assessment.

See key facts
A London consultant allergist reviewing an ISAC molecular allergy component profile

Key facts

  • 01

    Multiplex IgE, 112 components

    ImmunoCAP ISAC measures specific IgE against 112 purified and recombinant allergen components in a single chip assay.

  • 02

    A single blood sample

    One venous serum sample is all that’s required — no repeat visits, no cumulative skin-prick sessions.

  • 03

    Not affected by antihistamines

    Unlike skin-prick testing, in-vitro IgE measurement is unaffected by antihistamine use — no wash-out needed.

  • 04

    Primary vs cross-reactive

    Distinguishes genuine primary sensitisation from cross-reactivity driven by shared protein families.

  • 05

    Guides risk and immunotherapy

    Component patterns help stratify anaphylaxis risk and inform decisions on venom or food immunotherapy.

  • 06

    Consultant allergist reporting

    Interpreted alongside your clinical history by a consultant allergist — the chip is the input, not the answer.

The journey

From consultation to component profile — what happens, in order.

A consultant allergist frames the question, the chip provides the data, and the plan is built around your history.

  1. 01

    Before

    Consultant allergist consultation

    A structured allergy history — reactions, timing, triggers, co-factors — decides whether ISAC is the right test for you.

  2. 02

    Before

    Serum blood sample

    A single venous blood draw at the clinic or at home. No fasting, no medication wash-out.

  3. 03

    In the lab

    Chip-based multiplex analysis

    Your serum is applied to the ImmunoCAP ISAC biochip, testing IgE against all 112 allergen components in parallel.

  4. 04

    In the lab

    Result in 7–10 days

    The laboratory returns a quantitative component profile — reported in ISU-E units per component.

  5. 05

    After

    Component profile reviewed with history

    Your allergist maps each positive component against your clinical story — what’s real, what’s cross-reactive, what’s incidental.

  6. 06

    After

    Personalised avoidance plan

    A written plan: what to avoid strictly, what is likely safe, and how to handle cross-contact and dining out.

  7. 07

    After

    Structured follow-up

    Auto-injector training if indicated, review of immunotherapy candidacy, and scheduled review of any evolving reactions.

Typical end-to-end: 7–10 days from blood draw to reported component profile.

What it shows

The component families the ISAC chip reports on.

Each component tells a different story — risk-carrying storage proteins on one side, benign cross-reactive panallergens on the other.

  • Peanut Ara h 2

    The single strongest molecular marker of systemic anaphylaxis risk in peanut allergy.

  • Tree nut components

    Cor a 14 (hazelnut), Jug r 1 (walnut), Ana o 3 (cashew) — storage proteins carrying real anaphylaxis risk.

  • PR-10 cross-reactive proteins

    Bet v 1 homologues that drive pollen-food (oral allergy) syndrome — usually mild, rarely systemic.

  • Profilins

    Panallergens across fruits, vegetables and pollen — cause cross-reactivity, rarely serious reactions.

  • Storage proteins

    Heat- and digestion-stable proteins in nuts, seeds and legumes — the anaphylaxis-relevant class.

  • Bee and wasp venom components

    Api m 1 vs Ves v 5 discrimination — informs venom immunotherapy selection for systemic reactors.

  • Latex components

    Hev b 1, 3, 5 and 6.02 — separates true latex sensitisation from cross-reactivity with fruit profilins.

  • Red flag: high-risk component + anaphylaxis history — adrenaline auto-injector and specialist follow-up

    A positive Ara h 2 or storage protein with prior anaphylaxis means an adrenaline auto-injector and consultant follow-up.

Next steps

What the ISAC result unlocks.

The component profile is only useful if it changes what you do next — an avoidance plan, an auto-injector, a referral, a challenge.

  • Personalised avoidance plan

    A written, component-specific avoidance plan — what to strictly avoid and what is likely safe.

  • Adrenaline auto-injector

    Prescription and hands-on training where anaphylaxis risk is confirmed by history and component profile.

  • Antihistamines / nasal steroids

    Symptomatic control for aeroallergen-driven rhinitis, conjunctivitis and oral allergy symptoms.

  • Oral immunotherapy referral

    Referral for peanut or milk OIT in appropriately selected paediatric and adult patients.

  • Venom immunotherapy

    Subcutaneous immunotherapy for confirmed bee or wasp venom systemic reactors — component-guided.

  • Occupational allergy management

    Workplace exposure review, PPE, and, where needed, occupational health redeployment advice.

  • Supervised food / drug challenges

    Hospital-based challenges to confirm or exclude clinical reactivity where the component profile is ambiguous.

  • Structured allergist follow-up

    Scheduled review of new reactions, evolving sensitisation and immunotherapy response.

Red flags

When ISAC is not optional — it’s indicated.

Presentations where molecular allergen component testing meaningfully changes management, and where a consultant allergist opinion should not be delayed.

  • Anaphylaxis history

    Any prior systemic reaction — airway, breathing or circulation involvement — is a red flag requiring specialist input.

  • High-risk peanut Ara h 2

    A positive Ara h 2 markedly increases the probability of systemic reactions on re-exposure.

  • Multiple concurrent food allergies

    More than one clinically relevant food allergy raises the risk of accidental exposure and severe reactions.

  • Venom systemic reaction

    Any generalised reaction to a bee or wasp sting warrants venom component testing and immunotherapy assessment.

  • Latex allergy in healthcare workers

    Occupational latex sensitisation carries perioperative and workplace risk — component testing clarifies severity.

  • Occupational allergy

    Workplace-onset symptoms with a plausible exposure require component-level clarification and OH input.

  • Idiopathic anaphylaxis

    Unexplained anaphylaxis benefits from broad component screening to uncover hidden triggers.

  • Systemic mastocytosis differential

    Recurrent severe reactions with a low IgE profile should prompt tryptase testing to exclude mastocytosis.

  • Food-dependent exercise-induced anaphylaxis

    Omega-5-gliadin and other components help identify the wheat-dependent, exercise-triggered subgroup.

Frequently asked

Everything patients ask about the ISAC test.

What it is, how it differs from a standard allergy blood test, what a positive result means, and when it earns its place.

  • What is the ISAC test?

    ISAC (ImmunoCAP ISAC) is a multiplex allergy blood test that measures specific IgE against 112 purified and recombinant allergen components on a single biochip — a snapshot of molecular allergen sensitisation from one blood sample.

  • How is ISAC different from a standard allergy blood test?

    Standard specific-IgE tests measure IgE against whole allergen extracts. ISAC measures IgE against individual molecular components within those allergens — which is what lets it distinguish genuine primary sensitisation from cross-reactivity, and high-risk from low-risk patterns.

  • Do I need to stop antihistamines before the ISAC test?

    No. Because ISAC is a blood test, antihistamines do not affect the result. That is one of its practical advantages over skin-prick testing.

  • How long do results take?

    The chip is processed at a specialist laboratory and results are typically available within 7–10 days, then reviewed with you at a consultant allergist follow-up.

  • Does a positive ISAC result mean I am allergic?

    Not on its own. ISAC shows sensitisation — the presence of specific IgE. Whether that sensitisation causes real-world reactions is a clinical judgement made by your allergist against your history.

  • Is ISAC useful in unexplained anaphylaxis?

    Yes. Broad multiplex component testing often uncovers hidden or unsuspected triggers — omega-5-gliadin, LTPs, storage proteins or venom components — that targeted tests can miss.

Sources

Guidance and standards behind this page.

Reviewed by Pulse Atlas Editorial Board () · Published 2026-07-30 · Next review 2027-07-30 · ~5 min read

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