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Diagnosis & Specialist Care of Allergy & Clinical Immunology - Since 1982
Welcome to our page on Skin Prick Tests
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.
Safety and Comfort
Skin prick tests are very safe and well-tolerated by most people. The process is not painful, and the sensation is often described as mildly uncomfortable rather than painful. The small red bumps that appear (if you have a positive reaction) usually fade within a few hours. Importantly, this test does not involve the use of needles—only a small lancet is used to make the scratch.
No recovery time is needed and the patient can carry on with their day-to-day activities as before.
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.
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