Part of the London Allergy Clinic
Diagnosis & Specialist Care of Allergy & Clinical Immunology - Since 1982

Welcome to The Allergy Testing Clinic
Part of The London Allergy Clinc
We are experts in the testing, diagnosis and specialist treatment of all forms of Allergy. Our consultations rooms are based in Marylebone and High Barnet, where we have been treating patients for over 40 years.
Allergy Testing
Everything You Need to Know
Living with allergies can be challenging, but understanding your triggers is the first step to managing them effectively. Allergy testing plays a crucial role in identifying the substances that cause allergic reactions.
Below you will find some useful information about the various types of allergy tests. If you still have any questions, or would like to speak with one of our specialists, please get in touch.
Types of Allergy Tests
​A blood test​
However some allergies can only be investigated via a specific IgE test - such as wasp/bee or other insect stings. A blood test may also be preferred when the patient wishes to test a wider range of allergens in one go, which will not be covered by the skin prick test.
It is also particularly useful for molecular component testing, which allows allergies to be investigated to a more precise, forensic degree.
A skin prick test
​A skin prick test is considered the gold standard for aeroallergens. It is also particularly useful for more obscure allergies - where a blood test may not be available for the substance in question. A skin prick test can be used to test anything, provided the patient can bring a small sample of the product with them. This could be a specific meal that may have triggered a reaction; a certain sauce; cooked or uncooked fruits/vegetables or even a lip balm or other cosmetic product.
Each method has their unique benefits and should always be conducted alongside a doctor’s consultation to ensure accurate interpretation of the results. Here's everything you need to know about these essential tests.
Specific IgE Blood Tests

How Does Specific IgE Blood Testing Work?
This test measures the concentration of IgE antibodies in your blood in response to particular allergens. When your body encounters an allergen, IgE antibodies play a key role in triggering an allergic reaction. These antibodies stimulate mast cells to release histamine, leading to common allergic symptoms like itching, sneezing, and swelling.
How Is the Test Performed?
Specific IgE blood tests can target a single allergen or assess multiple allergens simultaneously. One of the most comprehensive tests available is the ALEX2 (Allergen Explorer) test, which can detect sensitivities to 295 different allergens, covering a wide array of food and environmental allergens.
A blood sample is required for specific IgE testing. This sample can be collected in two ways:
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Venous Blood Draw:
Healthcare professional will draw blood using a needle.
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Fingerprick Blood Sample:
In some cases, a capillary blood sample can be taken by pricking the finger.

Importance of Specialist Interpretation
While high IgE levels can indicate an allergic response, they do not confirm a diagnosis on their own. Given the complexity of the results, having them interpreted by an experienced clinician is essential. The test shows sensitisation to certain allergens, but further investigation, including a detailed clinical history and possibly a skin prick test, is required to confirm an allergy.
Proper interpretation helps avoid unnecessary dietary restrictions and ensures accurate diagnosis and management.
Skin Prick Testing
Skin prick testing is the most common and trusted method for diagnosing allergies. It’s widely used by allergy specialists to identify sensitivities to a range of airborne allergens (aeroallergens), including dog and cat dander, mould, house dust mites, and various pollens. Additionally, it’s an effective tool for testing food allergies. The process is quick, safe, and provides immediate results, making it an essential part of allergy diagnosis.

How Does Skin Prick Testing Work?
The test is simple and usually takes about 20 minutes from start to finish. Here’s what to expect:
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Preparation: A medical professional will apply small drops of allergens onto the skin of your forearm.
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Application: Using a small lancet (not a needle), they’ll gently scratch the skin where the droplets are placed. This allows the allergen to penetrate the skin’s surface.
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Reaction Observation: If you’re allergic to a substance, a small, itchy red bump (wheal) will develop at the site of the scratch. The size of this wheal is measured in millimetres to help determine the severity of the allergy. Typically, larger wheals indicate greater sensitivity.
Accuracy and Controls
To ensure the accuracy of the test, positive and negative controls are used:
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Positive Control
A drop of pure histamine is applied. This should always produce a red, itchy wheal, confirming that your body’s histamine response is functioning correctly.
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Negative Control
A drop of 100% saline is applied. This should produce no reaction at all.
Each allergen’s response is measured against the reaction to the pure histamine. If the wheal from an allergen is smaller than the histamine wheal, the result is considered borderline positive, and further investigation might be needed before confirming an allergy diagnosis.
Considerations and Limitations
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Dermatographism: Occasionally, some patients might show a reaction even to the saline control. This could indicate dermatographism, a common condition where any scratch or pressure on the skin causes a wheal to form. If you have this condition, it’s best to delay the test until the condition subsides, as it could distort the results.
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Recent Allergic Reactions: Skin prick testing should not be performed within 4-6 weeks following a significant allergic reaction, as this might lead to a false negative result.
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Test Range: The test can assess 10-15 different allergens at a time, making it ideal for patients who have a good idea of what might be triggering their symptoms and want to confirm or exclude specific allergens.


The Role of Skin Prick Testing in Allergy Diagnosis
When performed correctly, skin prick testing is an invaluable tool for clinicians. It helps confirm suspicions about what’s causing allergic reactions and is particularly useful for pinpointing aeroallergens and food allergies. Though it has some limitations, the test remains a gold standard in allergy diagnostics due to its reliability, safety, and the immediacy of its results.
Other Services
At The London Allergy Clinic we see adults, adolescents & children suffering with a number of allergic conditions including hay fever, food allergies, house dust mite allergies, urticaria (hives), sudden-onset swelling (angioedema) and more. We also see patients suffering with other immunological conditions.
We offer a comprehensive diagnostic and treatment service with specialist clinicians.