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. There are two main types of tests that are reliably used for this purpose:
skin prick testing; and
specific IgE (blood) testing.
Both methods have their unique benefits and should always be conducted under a doctor’s supervision to ensure accurate interpretation of the results. Here's everything you need to know about these essential tests.
Skin prick testing
How it works
Skin prick testing is a straightforward and commonly used method to test for allergies, particularly for aeroallergens like pollens, house dust mites, and animal dander. During the test, a small amount of the allergen, concentrated in liquid form, is placed on the patient's forearm. A tiny scratch is then made in the skin where the droplet is located. If the patient is allergic to the substance, a red, raised, itchy bump (called a wheal) will appear within 15-20 minutes.
The test does not draw blood and it does not require any recovery time - the patient can straight away continue with their day as usual.
Interpreting the Results
The size of the wheal can correlate with the severity of the allergy. A larger wheal generally indicates a stronger allergic reaction. However, it’s important to note that the presence of a wheal alone doesn’t confirm an allergy diagnosis. A doctor will consider the results alongside the patient’s clinical history and symptoms.
Advantages and Limitations
Skin prick tests are particularly reliable for identifying aeroallergens, but they are limited in terms of the number of allergens they can test at once. Typically, a skin prick test will assess 10-15 different allergens at a time. For a comprehensive test which examines a larger panel of allergens in one go, consider a specific IgE blood test. Skin prick testing is safe for patients of all ages, including children. Although it is not recommend to allergy test very young babies before they have been weaned.
Specific IgE: Blood Allergy Testing
How it works
A specific IgE test measures the amount of immunoglobulin E (IgE) antibodies in the blood in response to particular allergens. High levels of IgE indicate that the body is sensitised to the allergen, suggesting a potential allergy.
Interpreting the results
While high IgE levels can indicate an allergic response, they do not confirm a diagnosis on their own. 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.
Advantages and Limitations
Specific IgE testing is highly useful for food allergies and can perform a broader range of tests compared to skin prick testing. The ALEX test, for instance, can test for up to 295 different allergens. This method is also particularly advantageous for molecular allergen testing (component testing). Specific IgE testing is safe for patients of all ages, including children. Although it is not recommend to allergy test very young babies before they have been weaned.
Molecular Component Testing
Understanding Molecular Allergens
Component testing delves deeper into the specifics of an allergen by examining its individual protein components. For example, a peanut allergy can vary in severity depending on which specific proteins within the peanut are causing the reaction. Component testing can identify these proteins, providing a more detailed understanding of the allergy.
Why it Matters
Understanding which proteins, specifically, within an allergen are triggering the allergic reaction can help to predict the potential severity and frequency of reactions, aiding in better preparation and treatment plans.
Choosing The Right Test
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.
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.
The Role of Clinical History
Both skin prick and specific IgE tests should be interpreted in the context of a detailed clinical history. Your allergist will consider your symptoms, the timing of reactions, and any other relevant factors to make an accurate diagnosis. It's essential to have a thorough discussion with your doctor about your symptoms and medical history before and after testing.
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