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Allergy testing

Component-resolved diagnostics

Advanced allergy blood tests that identify which exact protein within a food you react to - and how risky that reaction is likely to be.

Key facts

At a glance

  • Preparation: none - it is a standard blood test and antihistamines do not affect it.

  • What it shows: antibodies to individual proteins (components) within an allergen, such as Ara h 2 in peanut, which separate high-risk from usually mild patterns.

  • Why it helps: whole-allergen tests cannot distinguish dangerous storage-protein allergy from mild pollen cross-reactivity - components can.

  • Results: typically back within one to two weeks privately.

  • Follow-up: a consultant allergist translates the component pattern into practical advice about avoidance, adrenaline auto-injectors and food challenges.

The full picture

What this test involves, and how to get it

Component-resolved diagnostics takes allergy blood testing a level deeper. Instead of measuring antibodies against a whole peanut or hazelnut extract, it measures them against the individual proteins inside - and those proteins behave very differently. Antibodies against heat-stable storage proteins such as Ara h 2 in peanut point towards genuine, potentially severe allergy, while antibodies against pollen-related proteins such as PR-10s usually mean mild mouth itching from cross-reactivity with birch pollen. The same blood sample can therefore change a plan entirely: from strict avoidance and adrenaline pens to reassurance, or the other way round.

Component testing is most useful in nut, peanut, egg, milk and wheat allergy, in unexplained anaphylaxis, and before deciding whether a supervised food challenge is safe. On the NHS it is available through specialist allergy centres, usually after standard tests have raised questions. Privately, consultant allergists can request components alongside initial blood work, with results in one to two weeks and appointments typically available within days. Interpretation is genuinely specialist territory - the patterns matter more than any single number - so results should always come with a consultation.

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 Component-resolved diagnostics.

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

  • What does the Component-resolved diagnostics measure?

    The Component-resolved diagnostics measures a specific substance or marker in your blood that helps doctors assess how a particular organ or system in your body is functioning. It's usually interpreted alongside your symptoms, medical history and other results rather than in isolation. Your GP or specialist can explain exactly what your individual result means for you.

  • Why would a doctor request Component-resolved diagnostics?

    Component-resolved diagnostics is typically requested when a doctor wants to investigate specific symptoms, monitor an existing condition, or check for an underlying imbalance that could explain how you're feeling. It may also be included as part of a broader health check or a more targeted diagnostic panel. Your clinician will explain why it's relevant to your particular situation before requesting it.

  • Do I need to prepare for Component-resolved diagnostics?

    Some blood tests require fasting, a specific time of day, or a pause in certain medications, while others need no preparation at all. Because requirements vary and we don't want to guess incorrectly for this specific test, always check the preparation instructions given at booking or ask the clinic directly. Turning up prepared, if preparation is needed, avoids having to rebook and wait again.

  • What happens when I have Component-resolved diagnostics?

    Most blood tests involve a short, straightforward appointment where a trained phlebotomist takes a small sample from a vein in your arm. The process usually takes only a few minutes and most people experience nothing more than a brief pinch. You can typically resume normal activities straight away.

  • Does Component-resolved diagnostics hurt or carry any risk?

    A standard blood draw causes only brief discomfort at the needle site, with a small risk of bruising or light-headedness afterwards. Serious complications are rare, and staff are trained to make the process as comfortable as possible. Let the phlebotomist know if you've had problems with blood tests before, such as fainting, so they can take extra care.

  • How long does it take to get results?

    Private laboratories generally turn results around within a few working days, though some specialised tests take longer to process. You'll usually be told an expected timeframe when you book, and results are typically reviewed by a doctor before being shared with you. If a result needs urgent attention, the clinic will usually contact you sooner rather than making you wait for a routine follow-up.

  • What does an abnormal Component-resolved diagnostics result mean?

    An abnormal result doesn't automatically mean something serious is wrong — levels can be affected by hydration, medication, recent illness, timing of the sample, or normal individual variation. A doctor will look at the size and pattern of any abnormality alongside your symptoms and other results before deciding whether further tests, monitoring, or treatment are needed. It's always worth discussing an abnormal result with a doctor rather than trying to interpret it alone.

  • Can I get Component-resolved diagnostics on the NHS, or is it better to go private?

    Many blood tests are available on the NHS, but routine, non-urgent testing can involve a wait for a GP appointment and then for the sample and results. Private testing is typically available within days, often with same-week appointments and results reviewed by a specialist, which can be useful if you want reassurance quickly or your GP hasn't recommended the test. Cost for private testing varies by clinic and whether it's a standalone test or part of a wider panel.

  • How accurate and reliable is Component-resolved diagnostics?

    When carried out by an accredited laboratory, this type of blood test is generally considered a reliable way to measure the substance in question. As with any single blood test, results can vary slightly from day to day and are best interpreted in the context of a full clinical picture rather than as a one-off number. If a result seems unexpected, doctors will often recommend repeating the test to confirm it before acting on it.

  • How do I book Component-resolved diagnostics privately?

    You can typically book a private blood test online or by phone, often without needing a GP referral, and be seen within a few days. Results are usually reviewed by a doctor who can explain what they mean and recommend any next steps or further investigations. Get in touch with the clinic to check current availability and what's included with the test.