Molecular allergy diagnostics · London
Component-resolved allergy testing (ISAC / ALEX) - private in London
A single blood test that measures specific IgE to individual molecular allergen components - separating the sensitisations that carry real anaphylaxis risk from the cross-reactive ones that do not. Booked with a consultant allergist, not a walk-in lab.
112 · 295
ISAC components · ALEX allergens
One blood draw. A molecular map of what you are actually allergic to.
What it is
Not "are you allergic?" but "which molecule are you allergic to?"
Conventional allergy blood tests measure IgE to a whole allergen extract - a mixture of dozens of proteins. Component-resolved diagnostics (CRD) instead measures IgE against the individual purified or recombinant proteins within that source.
Why the molecule matters
Within a single peanut, some proteins (storage proteins such as Ara h 2 and Ara h 6) are heat-stable, digestion-resistant and strongly associated with anaphylaxis. Others (PR-10 proteins such as Ara h 8) look almost identical to birch pollen and typically cause only oral itch after raw exposure. A whole-extract test cannot tell them apart. A component test can.
Primary vs cross-reactive sensitisation
Component panels distinguish genuine primary sensitisation (the immune system has directly recognised a food or venom) from cross-reactive sensitisation (pollen antibodies happen to bind a similar protein in fruit, nut or latex). The first often carries real risk. The second usually does not.
Assays available in the UK
Four testing platforms, one blood sample.
Which one is right depends on the clinical question, the patient’s age, and whether you already know which allergen is under suspicion.
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ImmunoCAP ISAC 112
Semi-quantitative microarray measuring specific IgE to 112 allergen components from 51 sources. The long-established UK reference panel.
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ALEX2 (Allergy Explorer)
Macroarray covering 295 allergens: 178 whole extracts plus 117 molecular components. Broader coverage, useful for polysensitised patients.
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ImmunoCAP ISAC-E
Focused ISAC variant for a select subset of components. Sometimes offered where the full 112 panel is not warranted.
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Single-component ImmunoCAP
Quantitative singleplex tests for one component at a time (e.g. peanut Ara h 2, hazelnut Cor a 14). Best when the clinical question is narrow.
When it adds value
The clinical scenarios where CRD changes the plan.
Component testing is not a screening tool. It is most useful when history and skin prick results leave a genuine clinical question unanswered.
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Multiple positive skin prick tests
Component testing separates genuine primary sensitisation from cross-reactive pollen-driven positives, sharpening risk stratification.
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Peanut allergy with a borderline history
Ara h 2 and Ara h 6 identify high-risk peanut allergy; isolated Ara h 8 usually points to milder pollen cross-reactivity.
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Tree nut characterisation
Hazelnut, walnut and cashew components help distinguish those at risk of anaphylaxis from those who react only to raw nut with oral symptoms.
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Respiratory allergy before immunotherapy
Confirming genuine sensitisation to major grass (Phl p 1, Phl p 5), birch (Bet v 1) or house dust mite components before starting a 3-year course.
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Alpha-gal (red meat) after tick bite
Delayed reactions to mammalian meat: alpha-gal specific IgE confirms the diagnosis when history is suggestive.
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Latex-fruit and LTP syndromes
Component panels separate genuine latex allergy from cross-reactive positives, and flag lipid transfer protein sensitisation common in Mediterranean patients.
Key components
High-risk vs low-risk molecules, at a glance.
The clinically important split within the most commonly tested foods and pollens.
| Source | High-risk component | Cross-reactive / lower-risk |
|---|---|---|
| Peanut | Ara h 2, Ara h 6 (storage proteins) - systemic reaction risk | Ara h 8 (PR-10, birch cross-reactive) - usually oral only |
| Hazelnut | Cor a 14 (storage protein) - systemic risk | Cor a 1 (PR-10) - pollen cross-reactive, oral symptoms |
| Egg | Gal d 1 (ovomucoid) - heat-stable, baked-egg reactive | Gal d 2 (ovalbumin) - heat-labile, often baked-tolerant |
| Milk | Bos d 8 (casein) - heat-stable, baked-milk reactive | Bos d 4/5 (whey) - heat-sensitive, often baked-tolerant |
| Birch pollen | Bet v 1 - major allergen, drives pollen-food syndrome | Bet v 2 (profilin) - pan-allergen, low clinical relevance |
| Timothy grass | Phl p 1, Phl p 5 - genuine grass sensitisation, immunotherapy candidate | Phl p 12 (profilin) - cross-reactive |
Cost in London
Honest ranges across our partner clinics.
Test fee, phlebotomy and consultant reporting are usually charged separately. We come back with firm figures within one working day.
| Test | Indicative range | Appointment time | Turnaround |
|---|---|---|---|
| ImmunoCAP ISAC 112 (full panel) | £450-£850 | Blood draw 15 min | 5-10 working days |
| ALEX2 (295 allergens) | £550-£950 | Blood draw 15 min | 7-14 working days |
| ImmunoCAP ISAC-E (focused) | £380-£650 | Blood draw 15 min | 5-10 working days |
| Targeted 3-5 component panel | £280-£450 | Blood draw 15 min | 3-7 working days |
| Single component (e.g. Ara h 2, Cor a 14) | £120-£250 | Blood draw 15 min | 3-7 working days |
| Allergist consultation to interpret | £250-£450 | 45-60 min | Same visit |
Where to have it
London providers we work with.
Samples are processed at Viapath, Synlab or specialist molecular allergy laboratories. What matters more than the lab is the consultant allergist who reports and acts on the result.
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The Portland Hospital Paediatric Allergy
HCA paediatric allergy service, Great Portland Street. Consultant-led ISAC and single-component testing for children.
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HCA The Wellington Hospital
Adult and paediatric allergy clinics, St John's Wood. ISAC 112 and ALEX2 both available through affiliated laboratories.
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Great Ormond Street International & Private Care
Tertiary paediatric allergy service. Component testing routinely integrated with oral food challenge planning.
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London Allergy Clinic (Harley Street)
Consultant allergist-led. ISAC, ALEX2 and single-component ImmunoCAP with same-day phlebotomy.
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Chelsea and Westminster Private Care
NHS-linked private allergy service, adult and paediatric. Component testing routed to Viapath / Synlab.
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Cadogan Clinic
Sloane Street clinic offering ISAC and ALEX2 alongside skin prick testing and challenge planning.
Turnaround
From blood draw to a plan.
- ISAC 112: 5 to 10 working days from the laboratory.
- ALEX2: 7 to 14 working days.
- Single-component ImmunoCAP: 3 to 7 working days.
- Consultation to interpret: booked once results are back, usually within a further week. This is the step that matters: raw component numbers without expert interpretation are of little use.
Related
Tests and treatments that pair with CRD.
Component testing rarely stands alone. These are the diagnostic and treatment pathways it most often feeds into.
FAQs
The questions patients actually ask.
If yours is not covered, send us a message. We will come back within one working day.
ISAC or ALEX - which should I have?
ISAC 112 is the UK reference microarray with the longest track record and is what most consultant allergists request first. ALEX2 offers wider coverage (295 allergens, including many whole extracts) and can be useful in polysensitised or unusual cases. For a narrow clinical question - "is this peanut allergy real?" - a single-component ImmunoCAP is often more informative and cheaper than either.
Does component testing actually change management?
Yes, when used correctly. It can avoid an unnecessary oral food challenge, permit reintroduction of baked egg or baked milk, redirect patients away from ineffective immunotherapy, or confirm alpha-gal in delayed meat reactions. It is not a screening test and should be interpreted alongside history and skin prick results by an allergist.
Will my insurance cover it?
Most UK private medical insurers (Bupa, AXA, Vitality, Aviva, WPA, Cigna) cover component testing when medically indicated and requested by a consultant allergist with pre-authorisation. Screening use without symptoms is usually not covered.
How often should component testing be repeated?
For children with food allergy, every 12-24 months is typical to track natural resolution (particularly for egg, milk and wheat). For adults with stable respiratory allergy, repeat testing is rarely useful unless the clinical picture changes.
Do I need to fast or stop antihistamines?
No fasting is needed for a blood test. Antihistamines do not affect specific IgE results, so you can continue them (unlike skin prick testing, where they must be stopped for 5-7 days).
Can children have this test?
Yes. Component testing is particularly valuable in children because it can be done from a single blood draw when skin prick testing is distressing, and it guides decisions about oral food challenge and baked-egg or baked-milk reintroduction.
Ready to book?
Tell us the clinical picture. We match you to the right panel and the right consultant.
One concierge, from first message to the interpretation appointment. Free. We only take payment from clinics that meet our standards, never influence.