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Allergy testing

Specific IgE blood tests

Blood tests that measure allergy antibodies to individual foods, pollens and animals - useful when skin testing is impractical.

Key facts

At a glance

  • Preparation: none - antihistamines do not interfere with blood-based allergy tests, unlike skin prick testing.

  • On the day: a standard blood sample is taken and sent for analysis against the allergens your clinician selects.

  • What it shows: levels of IgE antibody against specific allergens, graded from undetectable to very high.

  • Results: usually back within a few days to two weeks privately, depending on the panel.

  • Follow-up: an allergist interprets levels in context - higher numbers make true allergy more likely but no single cut-off proves it.

The full picture

What this test involves, and how to get it

Specific IgE testing (formerly known as RAST) measures the amount of allergy antibody your immune system has made against individual substances - peanut, egg, grass pollen, cat dander and hundreds of others. It needs only a standard blood sample, works even when eczema or antihistamines make skin testing impractical, and carries no risk of provoking a reaction. Results are graded, and broadly the higher the level, the more likely a genuine allergy - but low positives are common in people who eat the food without any problem, so results should never be read as a verdict in isolation.

The choice of which allergens to test is where expertise matters most: broad untargeted panels generate confusing low positives, while a clinician-selected panel based on your history gives answers you can act on. NHS testing follows referral to an allergy service, where waits can be lengthy; privately, blood can be drawn within days at an allergy clinic or phlebotomy service, with results in one to two weeks and a consultant appointment to interpret them. Component-resolved testing, which looks at individual proteins within an allergen, can be added where the initial results are ambiguous.

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 Specific IgE blood tests.

Quick, plain-English answers to what people ask us most.

  • What is Specific IgE blood tests?

    Specific IgE blood tests 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.

  • Why would a doctor order Specific IgE blood tests?

    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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.