Allergy challenges explained: How they help confirm or rule out allergies
If you want confidence in your dietary or medication choices, an allergy challenge is the most reliable way to confirm or rule out an allergy.
Being told you might have a food or drug allergy can feel overwhelming. And while blood tests and skin prick tests are useful tests, they don’t always give clear answers. That’s where an allergy challenge comes in – it’s considered the most reliable way to confirm or rule out an allergy.
In this blog, we’ll explain what an allergy challenge involves, how it works, and what to expect, so you can feel more informed and confident about your care.
What is an allergy challenge?
An allergy challenge is a procedure used to confirm whether someone either tolerates or has an allergy to a specific substance (allergen). Because it carries the risk of inducing severe allergic reactions, it is always performed in a hospital by an allergy specialist.
During the challenge, you will be exposed to small, gradually increasing amounts of the suspected allergen while being closely monitored by an allergy consultant who is trained to identify and treat any reactions as soon as they occur.
Why do I need an allergy challenge?
You might need an allergy challenge if your GP or consultant suspects you have an allergy but other tests – such as skin prick or blood tests – haven’t provided clear answers. This procedure is considered the most accurate way to confirm or rule out an allergy, especially to foods or drugs.
It can also be used to confirm whether you’ve outgrown a known allergy, which is common in children with food allergies, or to confirm a food allergy following a positive allergy (skin prick or blood) test where you have never eaten that food.
By observing how your body reacts to small, controlled doses of the suspected allergen in a medical setting, your consultant can make a confident diagnosis and tailor your treatment plan accordingly. If a challenge confirms you are not allergic, this helps avoid unnecessary dietary or medication restrictions. Conversely, a challenge that confirms allergy can ensure you get the right care for your allergy needs.
What are the benefits of an allergy challenge?
An allergy challenge offers several important benefits, especially when other tests like skin prick or blood tests aren’t providing clear answers. This includes:
- providing conclusive results that allow you to feel more confident in your daily life
- confirming whether you are truly allergic to a specific food or drug
- assessing whether a previously diagnosed allergy has resolved
- helping your consultant to create an informed treatment plan
Food allergy challenge
A food allergy challenge is a supervised test used to confirm or rule out a food allergy. It’s considered the gold standard for diagnosing food allergies and is always conducted within a hospital where emergency support is available in the event of a reaction.
Here’s what to expect:
- Pre-test preparation: Before the challenge, your consultant will review your medical history, perform a brief physical exam, and ensure any chronic allergic conditions (like asthma or eczema) are well controlled. You may be asked to stop taking antihistamines for a few days beforehand, as they can mask early symptoms.
- Initial assessment: On the day of the test, you’ll be checked to ensure you’re well enough to proceed. If you’re unwell, the test may be postponed.
- Step-by-step exposure: You’ll be given very small amounts of the suspected allergenic food to eat. The dose will be gradually increased every 15 to 30 minutes over several steps, usually up to 4 to 6 doses, until either a reaction occurs, or the final dose is reached with no reaction.
- Close monitoring: Both during and after each dose, you’ll be observed closely for any signs of an allergic reaction. If symptoms appear, the test will be stopped immediately, and appropriate treatment will be given.
- Post-test observation: If no reaction occurs, you’ll be monitored for a short period after the final dose to ensure you remain symptom-free.
- Results and next steps: If you tolerate the full amount without symptoms, it’s likely you are not allergic to that food. If a reaction occurs, your allergy will be confirmed, and your consultant will advise on next steps.
Drug allergy challenge
A drug allergy challenge is a supervised test used to determine whether you are allergic to a specific medication. It is typically recommended when there is uncertainty about a past reaction, or when a medication is needed but listed as an allergy.
Here’s what to expect:
- Pre-test assessment: Before the challenge, your consultant will review your medical history, perform a brief physical exam, and ensure any chronic allergic conditions (like asthma or eczema) are well controlled. You may be asked to stop taking antihistamines for a few days beforehand, as they can mask early symptoms.
- Initial dose:You’ll be given a very small amount of the medication being tested. This will usually be given in increasing doses, 30 minutes apart.
- Monitoring: During and after each dose, you’ll be observed closely to monitor for any signs of an allergic reaction. If a reaction occurs, the test will be stopped immediately, and appropriate treatment will be given.
- Post-test observation:If no reaction occurs, you’ll be monitored for a short period after the final dose to ensure you remain well.
- Outcome: If you tolerate the medication without symptoms, it may be safely removed from your allergy list and prescribed in the future. If a reaction occurs, your allergy will be confirmed, and your consultant will advise on alternatives.
What are the risks of an allergy challenge?
While allergy challenges are generally safe when conducted in a controlled medical environment, they naturally carry some risks because they involve intentional exposure to a suspected allergen. These include:
- mild allergic reactions– such as itching, hives, sneezing, or mild stomach discomfort
- moderate allergic reactions– such as wheezing, coughing, or more pronounced skin reactions
- severe allergic reactions (anaphylaxis) – a rare but potentially life-threatening reaction which will be treated promptly
Some patients may also find themselves feeling very anxious about their allergy challenge, which is why it is important to maintain clear communication throughout the process.
Despite these risks, allergy challenges are considered safe when performed by trained professionals in a clinical environment. To reduce these risks, challenges are often graded, with multiple small doses administered, and emergency medications, including adrenaline, are prepared in advance and ready for use if needed. The benefits of obtaining a clear and accurate diagnosis often outweigh the potential risks, especially when the results can significantly improve quality of life and treatment planning.
How to access an allergy challenge
If you’ve been told you might have a food or drug allergy, but the diagnosis isn’t clear, your doctor may recommend an allergy challenge. This is the most accurate way to confirm or rule out an allergy.
The first step is to either speak with your GP and request a referral to an allergy specialist, or, if you’re paying for your own care, to book a consultation with an allergy specialist directly.
At your initial appointment, your allergy consultant will assess your symptoms, review any previous test results, and decide whether an allergy challenge is appropriate. These tests are only offered when clinically necessary.
If a challenge is recommended, this will take place at Cromwell Hospital in Kensington. Your consultant will carry out a full assessment to ensure the test is safe and suitable for you.
How to access an allergy challenge
At Cromwell Hospital, we provide a broad range of allergy challenges for both food and drugs. These include:
- peanuts
- eggs
- milk
- sesame
- wheat
- penicillin
- anaesthetic
You will need an initial consultation with an allergy specialist to determine whether an allergy challenge is right for you.
If you have received a referral from your GP and are using private medical insurance, please contact us on 020 7460 5700 to book your appointment.
If you are paying for your own care, you don’t need a GP referral. Simply contact our Self-Pay team on 020 7244 4886 to book a consultation with an allergy specialist directly.
