Anaphylaxis investigation (Specialist allergy assessment after anaphylaxis)
A specialist assessment after a severe, whole-body allergic reaction (anaphylaxis) to try to find the trigger, confirm the diagnosis and plan how to stay safe in future.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- It tries to find the trigger and confirm the diagnosis after a severe allergic reaction — but the cause is not always identified.
- Your detailed account of what happened matters more than any single test; tests are interpreted alongside the story, never on their own.
- Everyone who has had suspected anaphylaxis should be referred to a specialist allergy service and, in the meantime, offered adrenaline auto-injectors — if you are prescribed them, carry two in-date devices at all times.
- A good investigation ends with a written emergency plan, training in using adrenaline, and clear advice on what to avoid.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Can identify a likely trigger so you know what to avoid
Using broad 'allergy screen' panels without a clear history — these generate misleading positives and are not how anaphylaxis is investigated.
Skin prick results are read after about 15–20 minutes. Any small bumps settle within an hour or so.
A written, personalised emergency action plan covering symptoms and adrenaline use.
Skin prick results are read after about 15–20 minutes. Any small bumps settle within an hour or so.
You should leave with adrenaline auto-injectors if appropriate — usually two, to carry at all times — training in...
Specific IgE blood results and any baseline tryptase result come back and are interpreted alongside your history.
A supervised challenge test, if planned, is done on another day in hospital and may take several hours including...
What is an anaphylaxis investigation?
Anaphylaxis is a severe, sometimes life-threatening allergic reaction that affects the whole body. It can cause breathing problems, a drop in blood pressure, collapse, swelling, and a widespread rash. After a suspected episode, a specialist tries to work out what caused it and how likely it is to happen again.
The investigation is usually led by an allergy specialist or clinical immunologist. It starts with a careful, detailed story of exactly what happened — what you ate, took, touched or were exposed to, how quickly symptoms came on, and what helped. This history is the most important part. Tests are then chosen to support or rule out particular triggers, not used as a fishing expedition.
Tests may include blood tests for a chemical called tryptase (taken in the hours after a reaction, and sometimes a baseline level later), skin prick tests, blood tests for specific IgE (allergy antibodies), and, in selected cases, a carefully supervised challenge test in hospital.
The aim is a clear plan: what to avoid, how to recognise a reaction early, when and how to use adrenaline, and what to do in an emergency. Sometimes no single trigger is found — this is called idiopathic anaphylaxis — and the plan then focuses on emergency treatment and follow-up.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Skin prick test vs specific IgE blood test
| Feature | Skin prick test | Specific IgE blood test |
|---|---|---|
| Where done | In clinic, on the skin | Blood sample sent to lab |
| Speed of result | About 15–20 minutes | Days to weeks |
| Affected by medicines | Antihistamines must be stopped first | Not affected by antihistamines |
| What a positive means | Sensitisation, read with history | Sensitisation, read with history |
Neither test alone diagnoses or rules out anaphylaxis. A positive result without matching symptoms can be misleading, and a negative result does not always exclude a trigger.
Preparing for your test
- Write down everything you can remember about the reaction: date, time, what you ate, drank, took or touched in the hours before, how fast symptoms started, and what treatment was given.
- Bring any records from the emergency visit, including any tryptase blood results taken at the time.
- Bring a full list of your medicines, supplements and any adrenaline auto-injector you already have.
- Ask whether you need to stop antihistamines before skin prick testing, and for how long, as they can mask the result.
- Note any patterns: reactions linked to exercise, certain foods, stings, medicines, or other reactions in the family.
- Keep packaging or photos of any food, medicine or product you think was involved.
- Do not deliberately re-expose yourself to a suspected trigger to 'test' it at home — this can be dangerous.
What happens
The appointment usually starts with a long, detailed conversation about the reaction and your wider health. The specialist is building a timeline to spot the likely trigger.
Skin prick testing, if done, involves placing drops of test solutions on your forearm and gently pricking the skin through each drop. After about 15–20 minutes the specialist measures any small bumps. Blood may be taken for specific IgE tests, which are sent to a laboratory.
If a tryptase level was taken during the reaction, it is reviewed; a separate baseline sample may be arranged. In selected cases, a supervised challenge is planned for another day in a hospital setting with resuscitation facilities and staff trained to treat reactions.
Before you leave, the specialist should explain what has been found so far, give or review your adrenaline auto-injectors — you should have two to carry at all times if they are prescribed — show you and your family how to use them, and provide a written emergency plan.
Is this test right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- Using broad 'allergy screen' panels without a clear history — these generate misleading positives and are not how anaphylaxis is investigated.
- Home or commercial 'allergy tests' (such as IgG food panels or hair analysis), which are not validated and can cause harmful, unnecessary avoidance.
- Skin prick testing while taking antihistamines, which can hide a true reaction.
- Relying on testing alone when the priority is an emergency plan and adrenaline.
Delay or rearrange if…
- You are currently unwell or recovering from the acute reaction and not yet stable.
- You cannot safely stop antihistamines before skin prick testing.
- Key information from the emergency episode (such as the timed tryptase result) is missing and can still be obtained.
- A challenge test is being considered but full resuscitation facilities are not available.
Alternatives to discuss
- Careful trigger avoidance and an emergency plan while awaiting full assessment.
- Component-resolved (molecular) testing in specialist hands for selected triggers.
- Referral to a clinical immunology service if a mast cell disorder or immune cause is suspected.
- Watchful follow-up where the episode was mild or a clear single trigger is already obvious.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Can identify a likely trigger so you know what to avoid
- Confirms or questions whether the episode was truly anaphylaxis
- Provides a clear, written emergency plan and adrenaline training
- Helps judge the risk of future reactions
- Can reassure you about triggers that are unlikely to be the cause
- Connects you with specialist follow-up and education
Risks & complications
- Mild itching or small bumps after skin prick testing that settle quickly
- Bruising or discomfort from blood tests
- Anxiety or distress when revisiting a frightening event
- The trigger is not identified, which can feel unsatisfying
- A positive test that does not match your symptoms, causing confusion or unnecessary avoidance
- A negative test that misses the real trigger (false reassurance)
- Needing repeat visits or further tests to reach an answer
- A more significant allergic reaction during skin prick testing or, more relevantly, during a supervised challenge test
- Incidental findings that lead to more testing
The biggest risks are not from the tests themselves but from misreading them. A positive skin prick or IgE test only shows sensitisation, not allergy, and acting on it without the clinical story can lead to wrong, even harmful, avoidance. Challenge tests carry a real risk of reaction and must only be done where reactions can be treated immediately. Ask how each result will change your plan, and what happens if the cause is never found.
Published figures to discuss
Reliable headline percentages for 'finding the cause' are hard to quote because results depend heavily on the trigger, the timing of tests and how carefully the history is taken. False positives are common with broad testing, and a negative test does not always rule a trigger out. Rather than invent figures, this guide describes the pattern: tests are most useful when targeted, and idiopathic (no identified cause) anaphylaxis is a recognised outcome in a meaningful minority of people.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Acute tryptase sample missing the diagnostic window | Common practical problem | Tryptase is most useful when taken soon after symptoms, often around 1 to 2 hours and within 4 hours, with a later baseline for comparison. | Guide sourcesClinical context |
| Normal tryptase during true anaphylaxis | Possible, especially in food-triggered reactions | A normal tryptase does not rule out anaphylaxis; airway, breathing and circulation symptoms remain decisive. | Guide sourcesClinical context |
| No trigger found after full investigation | A minority of cases are idiopathic | Even without a trigger, the emergency plan and adrenaline training still matter. | Guide sourcesClinical context |
| Underlying mast-cell disorder after severe or recurrent anaphylaxis | Uncommon but important | Raised baseline tryptase, sting reactions, flushing, syncope or osteoporosis may prompt mast-cell work-up. | Guide sourcesClinical context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is usually no physical recovery from the investigation itself. 'Afterwards' is mostly about getting and understanding your results, your emergency plan and your follow-up.
- Mild, short-lived itching or bumps where skin prick tests were done
- A bruise at the blood test site
- Feeling emotionally drained after discussing a frightening reaction
- Waiting a while for blood results before a full picture emerges
- Some uncertainty if no single trigger is confirmed
Aftercare
- Carry two in-date adrenaline auto-injectors with you at all times if you have been prescribed them, and check the expiry dates.
- Keep your written emergency plan somewhere accessible and share it with family, friends, school or work.
- Make sure you and those around you know how and when to use adrenaline and to call 999.
- Avoid any confirmed or strongly suspected trigger while you wait for full results.
- Do not stop avoiding a known trigger on the basis of a single negative test without specialist advice.
- Attend follow-up so results can be explained and your plan updated.
- Consider a medical alert bracelet or card if advised.
- Timeline of the reaction written down
- Emergency and hospital records gathered
- Current medicines and supplement list ready
- Existing adrenaline auto-injector brought to clinic
- Antihistamine-stopping advice checked before skin testing
- Packaging or photos of suspected triggers kept
- Questions for the specialist noted
⚠ Get urgent help if…
- Difficulty breathing, wheeze, or noisy breathing
- Swelling of the lips, tongue, throat or face
- A feeling of throat tightness or trouble swallowing
- Sudden faintness, collapse or feeling that something is seriously wrong
- A widespread rash or hives with any of the above
- Symptoms returning hours after they first settled (a biphasic reaction)
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
A good result is a clear understanding of what happened and a practical plan to stay safe. Sometimes a specific trigger is confirmed; sometimes several are made very unlikely; and sometimes no single cause is found (idiopathic anaphylaxis), in which case the focus shifts to recognising and treating reactions promptly.
No test can guarantee you will never react again, and a normal or negative result does not always mean a trigger has been ruled out. The value of the investigation is in better decisions and a reliable emergency plan, not in absolute certainty.
Allergy patterns can change over time, and some childhood allergies are outgrown while new ones can appear. A plan made now may need review if you have another reaction, if your circumstances change, or if new information emerges. Adrenaline auto-injectors expire and must be replaced.
Related tests, treatments or support
The investigation often brings together several tests at once — history, skin prick tests, specific IgE and tryptase — because no single test is enough. Where a mast cell disorder or another condition is suspected, additional tests may be arranged with other specialists.
Follow-up & long-term care
You should be given, or referred to, a specialist allergy service that can confirm the diagnosis, interpret tests, train you in adrenaline use and provide ongoing education. Results are usually explained at a follow-up appointment or in a clinic letter, with advice on what to avoid and when to seek help. Auto-injectors should be reviewed and renewed before they expire.
- Replace adrenaline auto-injectors before the expiry date
- Review your emergency plan after any further reaction
- Keep family, carers, school or workplace updated on your plan
- Re-check allergy status with your specialist if your situation changes
Repeat, follow-on and what comes next
- Results may be inconclusive, needing repeat or additional tests on another day.
- A challenge test may be required to settle uncertainty when blood and skin tests disagree with the history.
- Allergy status can change over time, so the plan may need revisiting after future reactions.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- A written, personalised emergency action plan covering symptoms and adrenaline use.
- Demonstrated training in using an adrenaline auto-injector for you and your family.
- A clear named contact and route for questions and for renewing auto-injectors.
- A plan for follow-up and for reviewing the diagnosis if you react again.
- Honest discussion when the cause is not found, with a safety-first emergency plan.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- Length and complexity of the specialist appointment
- Number and type of tests (skin prick, specific IgE blood tests, baseline tryptase)
- Whether a supervised challenge test in hospital is needed
- Laboratory fees for blood tests
- Provision and training for an adrenaline auto-injector
- Follow-up appointments and written reports or plans
- Whether further specialist input (for example for a suspected mast cell disorder) is required
- The specialist (allergist or clinical immunologist) consultation fee
- Which tests are included and the laboratory fees for each
- Whether a supervised challenge test, and its hospital costs, may be needed
- Cost of any adrenaline auto-injector and training
- Follow-up appointment and written emergency plan
- What happens, and what it costs, if results are inconclusive and more tests are needed
- Cancellation policy
On the NHS? Specialist assessment after suspected anaphylaxis is recommended and available on the NHS; private clinics are sometimes used for speed, choice or a second opinion.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Ordering large untargeted allergy panels and treating every positive as a real allergy.
- Not explaining that sensitisation on a test is not the same as clinical allergy.
- Failing to provide an adrenaline auto-injector and training before the specialist appointment.
- No written emergency plan, or no explanation of what to do if no trigger is found.
- Suggesting a normal test means you are 'cured' or can stop carrying adrenaline.
Marketing red flags
- Claims that a single blood test or panel can 'find all your allergies'.
- Promotion of unvalidated tests such as IgG food intolerance panels for anaphylaxis.
- Promising a definite trigger will always be identified.
- Selling broad avoidance diets off the back of test results without a clinical history.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- Based on my story, what do you think is the most likely trigger?
- Which tests are you doing, and what will each result change?
- What happens if the tests are normal, positive, or inconclusive?
- Do I need an adrenaline auto-injector, and can you train me and my family to use it?
- What exactly should I avoid while we wait for results?
- Could this be idiopathic anaphylaxis, and what does that mean for me?
- When and how will I get my results and a written emergency plan?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my test, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this test not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Can I have this investigation on the NHS?
Will the tests tell me exactly what caused my reaction?
Is the testing painful or risky?
Do I need to stop my antihistamines first?
What if no trigger is found?
Should I still carry adrenaline while I wait for results?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NICE NG258 — Anaphylaxis: assessment and referral after emergency treatment NICE QS119 — Anaphylaxis quality standard NHS — Anaphylaxis BSACI — Skin prick tests and specific IgE tests Resuscitation Council UK — Emergency treatment of anaphylaxis BSACI guideline — prescribing an adrenaline auto-injector NICE NG258 — Period of observation after anaphylaxis NICE NG258 — Information for the public
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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