If you suspect you have allergies and want a proper diagnosis, you'll quickly encounter three main testing options: skin prick testing, standard IgE blood panels, and the ALEX3 molecular blood test. Each has genuine strengths, and each is the right choice in different circumstances.
This guide explains exactly what each test does, how it works, its accuracy, what it can and cannot tell you, and which patients are best suited to each approach.
Quick Comparison
| Factor | ALEX3 Blood Test | Skin Prick Test | Standard IgE Blood Panel |
|---|---|---|---|
| Allergens screened | 295 in one test | Typically 20–40 | Typically 5–20 (requested specifically) |
| Antihistamines required to stop? | No | Yes (7–14 days) | No |
| Needles/skin contact required | Single blood draw only | Yes — multiple skin pricks | Single blood draw only |
| Molecular component testing (CRD)? | Yes — included | No | No (separate test required) |
| Suitable for children? | Yes | Yes (specialist setting) | Yes |
| Results affected by skin conditions? | No | Yes — dermographism, eczema affect results | No |
| Anaphylaxis risk during test? | None | Very low — resuscitation equipment required | None |
| Availability | Private clinics (Lambert Medical) | NHS allergy clinics, private specialists | NHS and private |
| Cost at Lambert Medical | Included in allergy testing package | N/A — not available at Lambert | Available as individual tests |
Skin Prick Testing
Skin prick testing (SPT) has been the clinical gold standard for allergy diagnosis for over a century. A small amount of allergen extract is placed on the forearm, and the skin is pricked through the extract. If you are sensitised to that allergen, a wheal (raised bump) develops at the prick site within 15–20 minutes.
Strengths of skin prick testing
- Immediate results — you can see the reaction within 20 minutes at the clinic
- High sensitivity for common inhalant allergens — particularly house dust mite, grass pollen, cat and dog epithelium
- Widely used clinically — large reference datasets exist for result interpretation
- Can test native foods — particularly useful for fresh fruit and vegetable allergies where commercial extracts may be less accurate (the "prick-to-prick" method)
Limitations of skin prick testing
- Antihistamines must be stopped 7–14 days beforehand — this is not always practical for patients with significant allergic symptoms
- Limited allergen panel — a typical SPT session tests 20–40 allergens; comprehensively screening hundreds of allergens would require multiple sessions
- Skin conditions affect results — dermographism (skin that weals easily), severe eczema, and urticaria all invalidate skin prick test results
- Requires specialist setting — should be performed where resuscitation equipment is available, as there is a very low risk of systemic reaction
- No molecular component data — cannot distinguish primary sensitisation from cross-reactivity without additional molecular testing
Standard IgE Blood Panels
Standard specific IgE blood tests measure antibody levels to individual allergens that your GP specifically requests. This is the most common allergy blood test available on the NHS and is the test you would receive following a GP referral.
When standard IgE testing is appropriate
- When you have a clear clinical history pointing to a specific allergen and simply need confirmation
- In children too young for skin prick testing
- When you're taking antihistamines that cannot be stopped
- As a targeted follow-up to a positive ALEX3 result requiring further characterisation
Limitations
- Narrow scope — you can only test allergens specifically requested; unexpected allergens are not detected
- No molecular component data — cannot distinguish cross-reactive from clinically relevant positives without CRD testing
- NHS availability — NHS testing is gatekept by GP referral and may test only 5–10 allergens at a time
ALEX3 Molecular Allergy Blood Test
The ALEX3 (Allergy Explorer 3) is the most advanced allergy blood test currently available. It simultaneously measures IgE sensitisation to 295 allergen sources and individual molecular allergen components, providing a complete allergy sensitisation map from a single blood sample.
What makes ALEX3 different
The key innovation in ALEX3 is component-resolved diagnostics (CRD). Rather than simply testing whether you react to "peanut" as a whole extract, ALEX3 measures your IgE response to the individual proteins within peanut — Ara h 1, 2, 3, 6, 8, 9. This distinction is clinically crucial:
- Ara h 2 sensitisation is associated with a high risk of severe systemic reactions to peanut
- Ara h 8 sensitisation alone is a cross-reactive protein associated with birch pollen; peanut reactions are typically mild oral symptoms only (oral allergy syndrome)
Without component testing, both patients would simply receive a positive "peanut allergy" result — one should be carrying an EpiPen, the other probably does not need to avoid peanuts at all.
Strengths of ALEX3
- Broadest available coverage — 295 allergens in one test, including foods, pollens, moulds, animals, dust mites, insects, and latex
- Component-resolved diagnostics — distinguishes primary sensitisation from cross-reactivity
- No antihistamine withdrawal — can be performed whilst on allergy medication
- No anaphylaxis risk — blood draw only, no allergen exposure
- Uncovers unexpected sensitisations — frequently identifies allergens patients had not considered
- Ideal for complex, multi-system allergy presentations
Limitations of ALEX3
- Requires GP interpretation — the volume of data means a GP review appointment is essential to contextualise results
- Not available on the NHS — currently a private test
- For some food allergens (particularly fresh fruits), skin prick-to-prick testing with fresh food may be more sensitive than blood testing
Which Test Should You Choose?
| Your Situation | Recommended Test |
|---|---|
| Unexplained multi-system symptoms (skin, gut, nose, eyes) with no obvious trigger | ALEX3 — comprehensive screening finds unexpected sensitisations |
| Seasonal hay fever, want to know which pollens | ALEX3 or standard IgE panel — both work well |
| Suspected peanut, tree nut, or shellfish allergy — need risk stratification | ALEX3 with CRD — distinguishes severe risk from mild cross-reactivity |
| On antihistamines you can't stop | ALEX3 or standard blood test — both unaffected by antihistamines |
| Severe eczema or dermographism | ALEX3 or blood panel — skin conditions invalidate SPT results |
| Known allergen, need confirmation only | Standard specific IgE — targeted and cost-effective |
| Considering immunotherapy (desensitisation) | Skin prick test at allergy specialist — required for immunotherapy planning |