Allergy test choice: consultation, skin prick or ALEX3

You have a sneeze that will not settle, a rash after a meal, a child who wheezes around cats, or a kit printout that named half the pantry, and search results then offer three doors at once: a consultation, a skin prick test, or a wide blood panel. Those are not interchangeable, and picking the wrong door is how people sit in a booked clinic with a reaction that needed an ambulance, or how they leave with a raised IgE and still have no idea whether they have a clinical allergy.

The allergy test choice at Medical Express Clinic is a consultant visit with Dr Scott Pereira at 117a Harley Street, or a named test when that test already fits. That is not a GP appointment, a pharmacy hay-fever chat, or an emergency department.

When is it 999 or A&E?

Call 999 or go to A&E if a reaction involves difficulty breathing, swelling of the tongue or throat, or collapse. If you have an adrenaline auto-injector, use it, then call 999. Medical Express Clinic is not an emergency service. A booked Harley Street slot cannot do that work. If that is happening now, stop reading and call 999.

When is a GP the right person?

Mild, well-controlled seasonal symptoms that already settle with pharmacy treatment may not need a consultant visit. A GP can take a history, look at what you have already tried, and decide whether a specialist opinion would help.

This clinic is consultant immunology, which is a different appointment from the GP service in the same building. If nobody has yet taken a basic history of a mild, pharmacy-responsive hay-fever season, start with a GP rather than a 290-allergen panel.

You do not need a GP referral to see Dr Pereira. Do not use an allergy booking as a way of skipping a GP when the problem is a cough, a fever, or a medicine review. Those remain GP work.

When is a consultation the usual start?

For a suspected allergy whose cause is still unclear, the usual start is a consultation with Dr Scott Pereira, Consultant Immunologist, GMC 01524080, at 117a Harley Street.

He sees adults and children. Allergy consultations and skin prick testing run on Tuesdays from 14:00, with the last bookable window ending at 17:30.

People come with a rash they cannot pin to a food, with wheeze that might be dust or a pet, with swelling after an insect sting, with a child who reacts at school, or with a previous blood result that nobody has talked through. Those are consultant questions, not a reason to order every allergen in the catalogue before anyone has taken a history.

Allergy UK estimates that over 21 million adults in the UK have at least one allergy. NICE CG116, the guideline on food allergy in under 19s, is built around an allergy-focused clinical history first. Tests should be chosen and interpreted in that context, and the guideline does not cover food intolerance such as lactose intolerance. The same logic holds for adults here: Dr Pereira starts with what is happening, then decides whether skin prick testing, ALEX3, or a targeted IgE panel would help.

Children can be seen here. A parent or legal guardian attends with them. Dr Pereira chooses the method that is suitable, safe and acceptable for that child.

Medical Express Clinic has practised at 117a Harley Street since 1984 and is CQC-registered. Visits usually last 30 to 60 minutes. Testing can be done on the same visit when it is suitable.

When is skin prick testing the test?

Skin prick testing is for when you want results during the appointment, with Dr Pereira in the room. Small drops of allergen extract are placed on the forearm and the skin is lightly pricked. A raised wheal, when it appears, is usually visible within about 15 to 20 minutes, and results are discussed in the same appointment.

The visit includes the consultation and up to eight allergens. If you suspect a particular substance, you may bring a sample.

Stop all antihistamines three days, which is 72 hours, before skin prick testing. Some medicines other than antihistamines also affect skin tests, so list everything you take when you book. Continue all other prescribed medicines as usual, including asthma inhalers and nasal sprays. If you cannot stop antihistamines, say so when you book, because a blood test may then be the better method.

When is ALEX3 the test?

ALEX3 is one blood sample that screens sensitivity to 290+ allergens, including foods, pollens, animal dander, moulds, dust mites and insect venoms. Results typically arrive within five working days and include a written report, so it is not a same-day result.

ALEX3 can be booked as a blood test without a separate consultation when that is clinically appropriate. If you want Dr Pereira to take the history and choose the test, book the consultation. The wide panel fits a broad history, several organ systems, or a wish for that coverage rather than a short list of extracts on the arm.

ALEX3 and other blood panels do not require stopping antihistamines, which is often the deciding point for people who cannot pause hay-fever tablets, or for children for whom a blood sample is the more acceptable method. A raised ALEX3 line is still sensitisation, not a menu of foods to abandon.

When is a targeted IgE panel arranged?

Targeted IgE blood panels look at a defined group of allergens when the history already points in one direction: inhalants, a food group, insects, antibiotics, eczema-related allergens, or a children's panel. Those panels are arranged at the consultation. Results typically take two to five working days, depending on the panel.

A food panel is an IgE sensitivity test. It does not diagnose lactose intolerance or other non-immune food reactions. The gluten sensitivity panel is a sensitivity profile, not an intolerance diagnosis. If bloating, delayed gut symptoms, or a suspicion of intolerance is the whole story, an IgE panel is the wrong investigation. Suspected coeliac disease needs a tTG-IgA blood test while you are still eating gluten.

What does a raised result mean?

A raised result shows sensitisation. It is not, on its own, a diagnosis of clinical allergy. Sensitisation means the immune system has made IgE to that allergen. Plenty of people are sensitised without a clinical reaction, and plenty have convincing symptoms with a negative test to the thing they blamed. That is why a kit printout is not a diet sheet, and why a negative skin prick does not let you ignore a reaction that was severe.

Dr Pereira reads the finding against timing, organ systems, reproducibility, medicines, asthma, and any previous anaphylaxis. Avoidance, a change of medicine, or a decision that the result can be left alone all come after that reading.

Once a diagnosis is in place, treatment is a different visit. Avoidance of a confirmed allergen, a change of medicine, or allergen desensitisation when he judges it appropriate are agreed with him at a consultation. Omlyclo, a biosimilar of omalizumab (original brand Xolair), is a separate in-clinic treatment path when licensed criteria are met. Every dose is given in clinic by Dr Pereira only. It is not a substitute for finding the trigger, and it is not the reason to book a test.

What should you bring?

Bring a list of current medicines, previous allergy results, and photographs of a rash or swelling if that is part of the story. If you have a referral letter, bring that too. If you are coming for skin prick testing and you suspect a particular substance, bring a sample.

What helps beforehand?

Decide which door you are walking through before you book.

• Breathing difficulty, tongue or throat swelling, or collapse is 999, not Harley Street.
• Mild seasonal symptoms that already settle with pharmacy treatment can start with a GP.
• The consultation is the usual start when the cause is unclear.
• Stop antihistamines 72 hours before skin prick testing, and continue inhalers and nasal sprays.
• If you cannot pause the tablets, book the blood route, because ALEX3 and blood tests do not require stopping antihistamines.
• Bring medicines, previous results and photographs.
• If a child is coming, a parent or legal guardian attends, and Dr Pereira chooses the method.
• Tell the clinic if the story sounds more like intolerance than allergy, because a food IgE panel will not diagnose lactose intolerance.

What should you avoid?

Do not sit on breathing difficulty, tongue or throat swelling, or collapse because you have a clinic appointment later in the week.

• Do not treat a raised IgE as a diagnosis, and do not treat a negative test as a promise that a convincing reaction cannot return.
• Do not book a 290-allergen panel because you wanted a GP to look at mild hay fever, and do not book a GP because you wanted Dr Pereira to interpret a complex history.
• Do not arrive on antihistamines for skin prick testing.
• Do not stop inhalers or nasal sprays because you were told to stop hay-fever tablets.
• Do not read a food IgE result as lactose intolerance, and do not start a wide avoidance diet from a kit printout before anyone has compared the numbers with your symptoms.
• If you do want consultant allergy testing, the details sit on the private allergy testing page, or you can contact the clinic on 020 7499 1991.

Related guides: choosing between a children's GP, NHS 111 and A&E and when to see a private GP.