Allergy testing
Skin prick testing
The standard first test for immediate allergies: tiny drops of allergen placed on the forearm to see which cause a reaction.
Key facts
At a glance
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Preparation: antihistamines must be stopped for about 3-5 days beforehand, as they blunt the test - your clinic will confirm timings.
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On the day: drops of allergen extracts are placed on the forearm and the skin gently pricked; itching or a small bump appears within 15-20 minutes if positive.
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What it shows: sensitisation to airborne and food allergens such as pollen, dust mite, pets, nuts and shellfish.
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Results: available in the same appointment, interpreted alongside your history by the allergist.
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Follow-up: a consultant allergist or immunologist explains what a positive result means for you - sensitisation is not always clinical allergy.
The full picture
What this test involves, and how to get it
Skin prick testing is the workhorse of allergy clinics. Small drops of standardised allergen extracts - pollens, house dust mite, animal dander, moulds, foods - are placed on the forearm, and the skin beneath each drop is pricked with a fine lancet. If you are sensitised, a small itchy bump (a wheal) appears within 15-20 minutes and its size is measured against controls. The test is quick, safe in trained hands and only mildly uncomfortable. Crucially, a positive test shows sensitisation, not necessarily clinical allergy: the result must always be read alongside your actual symptoms, which is why history-taking comes first.
NHS skin prick testing is available through allergy and immunology clinics after GP referral, but capacity is limited in many regions and waits of several months are common. Privately, consultant-led allergy clinics offer appointments within days to a couple of weeks, with testing and interpretation completed in a single visit. Stop antihistamines in advance as instructed, and bring a written note of your reactions - what you ate or were exposed to, how quickly symptoms came on, and how severe they were - as this shapes which allergens are tested.
A quiet reminder
This guide is for information, not medical advice.
Your own clinician knows your history and can tell you which parts apply to you. Next review of this page: 2027-09-27.
Frequently asked
Common questions about Skin prick testing.
Quick, plain-English answers to what people ask us most.
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What is Skin prick testing?
Skin prick testing is a blood test that measures a specific substance or marker in your blood, giving your doctor useful information about how a particular system in your body is functioning. It is one of many tools used alongside your symptoms and history to build a fuller clinical picture. Your doctor can explain exactly why it is relevant in your case.
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Why would a doctor order Skin prick testing?
This test is typically requested to investigate specific symptoms, monitor an existing condition, or check for a deficiency or imbalance that could explain how you are feeling. It may also be used as part of a broader panel of related tests rather than in isolation. The result helps guide whether further tests, treatment, or simple monitoring is appropriate.
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Do I need to prepare for this test?
Some blood tests require fasting, a specific time of day, or pausing certain medications or supplements beforehand, while others need no special preparation at all. You will usually be told what applies to your specific test when it is booked. If you are unsure, it is worth checking with the clinic or lab in advance.
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What happens during the test?
A small blood sample is taken, usually from a vein in your arm, in a process that takes only a few minutes. It is generally straightforward and similar to any other routine blood draw. You can normally return to your usual activities straight afterwards.
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Does this test hurt or carry any risks?
A standard blood draw involves brief discomfort from the needle but is otherwise low-risk. Minor bruising at the site is the most common side effect and usually settles quickly. Let the person taking your sample know if you have a needle phobia or have had problems with blood tests before, as they can help make it more comfortable.
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How long do results take?
Results are typically available within a few days, though turnaround can vary depending on the specific test and laboratory used. You will usually be told when and how to expect your results at the time of testing. More specialised tests may occasionally take longer.
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What do abnormal results mean, and what happens next?
An abnormal result can have several possible explanations, from common and benign causes to conditions that need further assessment, and is best interpreted by a doctor alongside your symptoms and history. Depending on the finding, next steps might include repeating the test, further investigation, or referral to a specialist. Try not to draw firm conclusions from a number alone before speaking to a clinician.
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Is this test available on the NHS, or is it better to go private?
This test can often be arranged privately within days, with results reviewed by a specialist, whereas routine NHS access may depend on your GP agreeing it is clinically indicated and can involve a longer wait. Cost for private testing varies by provider. Many people choose the private route for speed and convenience, particularly if they are self-funding for reassurance rather than an urgent clinical concern.
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Is this test accurate and reliable?
Blood tests like this are well established and generally reliable when carried out by an accredited laboratory. Results can occasionally be affected by factors such as timing, recent illness, medication, or hydration, which is why doctors interpret a single result in context rather than in isolation. If a result seems unexpected, repeating the test is sometimes recommended.
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How do I book this test privately, and how quickly can I be seen?
You can typically book privately with or without a GP referral, and appointments, including blood draw and results review, are often available within a few days. A doctor will explain what your result means and advise on any next steps.