The ALEX3 Allergy Test is a broad blood screen covering around 300 allergen sources in one sample, including 218 molecular (component) allergens, 107 of them unique to this test, plus a total IgE measurement. It suits people with sneezing, skin reactions or a suspected food reaction who want a wide first look, using component detail to help distinguish true allergy from cross-reactivity. The test costs £413.75, plus a £50 blood-draw fee, with results in 3-4 days. Walk in or book online at 117a Harley Street, seven days a week.
A doctor may suggest this test for someone with recurring symptoms such as sneezing, itchy or watery eyes, hives or digestive upset, where the trigger is not obvious and a wide, component-level screen would help narrow it down.
It is also used when someone reacts to more than one type of exposure, since testing around 300 allergen sources at once, including 218 molecular components, can be more practical than several separate tests and can help distinguish a genuine allergy from cross-reactivity between related allergens.
Some people request it simply to understand their allergy profile for the first time, particularly if allergic symptoms have appeared later in life or changed over time.
No special preparation is needed for this test and fasting is not required. If you are taking antihistamines, mention this when you book, as your doctor may advise on timing, though the blood test itself is not affected in the way a skin-prick test would be.
A raised result against a whole allergen or a specific molecular component shows your immune system has produced antibodies to it. This is called sensitisation, and it does not always mean you will have a noticeable reaction on exposure, so results are not read in isolation.
The molecular component results can help a specialist work out whether a positive result reflects a genuine risk of reaction or cross-reactivity with a related, better-tolerated substance, but this interpretation needs clinical judgement rather than reading the report alone.
If you have had a severe reaction, such as difficulty breathing or swelling of the face or throat, seek emergency medical care rather than waiting for this test, and discuss any positive result with a doctor before making changes to your diet or environment.
To have results interpreted by a consultant immunologist, see the allergy clinic at Medical Express Clinic.
Written by Mr Stephen Lingam. Reviewed by Dr Scott Pereira on 24/09/2026.
It is a blood test that screens around 300 allergen sources, including 218 molecular component allergens, 107 of them unique to this test, plus total IgE, all from a single sample.
It measures antibodies against individual proteins within an allergen source rather than the whole substance, which can help a specialist tell a genuine allergy apart from cross-reactivity with a related item.
Usually not, since it is a blood test rather than a skin-prick test, but mention any antihistamine use when you book so your doctor can advise.
Results are typically available within 3-4 days of your blood being taken at 117a Harley Street.