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Blood test

Histamine and DAO test

Histamine and DAO test: what it measures, why a doctor orders it, how to prepare, and what a high or low result can mean - with private and NHS access routes in the UK.

Key facts

At a glance

  • What it measures: blood histamine and diamine oxidase (DAO), the enzyme that breaks dietary histamine down - marketed as a test for histamine intolerance.

  • Why it is ordered: when flushing, hives, headaches or gut symptoms after certain foods raise the question of histamine intolerance.

  • No fasting or special preparation is needed for this test on its own.

  • Reference ranges: the honest position is that these assays are poorly standardised and correlate weakly with symptoms - no UK guideline endorses them for diagnosing histamine intolerance. Every laboratory publishes its own interval, so the range printed on your report is the one that applies to you.

  • A raised result in histamine, or a low DAO, is suggestive at best - a supervised low-histamine diet trial with re-challenge remains the more reliable approach. A low result or normal pair of results does not exclude food-triggered symptoms.

  • Results typically take a few days to two weeks, because the sample is analysed in batches at a specialist laboratory.

The full picture

What this test tells you, and how to get it

The histamine and DAO test measures blood histamine and diamine oxidase (DAO), the enzyme that breaks dietary histamine down - marketed as a test for histamine intolerance. Doctors most often request it when flushing, hives, headaches or gut symptoms after certain foods raise the question of histamine intolerance. No fasting or special preparation is needed for this test on its own. The honest position is that these assays are poorly standardised and correlate weakly with symptoms - no UK guideline endorses them for diagnosing histamine intolerance, and reference intervals genuinely differ between laboratories, so no single number should be treated as a universal cut-off - your result is always read against the range printed on your own report. Broadly, a raised result in histamine, or a low DAO, is suggestive at best - a supervised low-histamine diet trial with re-challenge remains the more reliable approach, while a low result or normal pair of results does not exclude food-triggered symptoms, and either finding is interpreted alongside your symptoms, medication and other results rather than in isolation. Results typically take a few days to two weeks, because the sample is analysed in batches at a specialist laboratory.

In the UK there are two routes to this test. Your NHS GP can arrange it free of charge when it is clinically indicated, though getting the appointment, the blood draw and the follow-up discussion can add days to weeks depending on local demand. Privately, the histamine and DAO test can usually be booked within days - through a private GP, a walk-in phlebotomy clinic or a self-request home-testing service - almost entirely through private laboratories - worth weighing the cost against the limited evidence, and a dietitian-led elimination trial answers the question more dependably. A private result still deserves a clinician's interpretation: an isolated number without context is where most confusion about blood tests begins.

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. Reference ranges vary between laboratories - always read your result against the interval printed on your own report. Next review of this page: 2027-09-27.

Frequently asked

Common questions about Histamine and DAO test.

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

  • What is the histamine and DAO test?

    This test measures blood levels of histamine and diamine oxidase (DAO), the enzyme mainly responsible for breaking down histamine from food in the gut. It is sometimes used when histamine intolerance is being considered as an explanation for symptoms after eating.

  • Why would a doctor order this test?

    It may be considered if someone has recurring symptoms such as flushing, headaches, hives, or digestive upset after eating histamine-rich foods, once more common causes like food allergy have been ruled out.

  • Do I need to prepare for a histamine and DAO test?

    You may be asked to avoid antihistamine medications and certain high-histamine foods for a period before the test, as these can affect results. Follow the specific instructions given by your clinic, as protocols vary.

  • What happens during the test?

    It is a blood test, taken in the same way as a routine blood sample.

  • How long do results take?

    Turnaround varies by laboratory, and can range from a few days to a couple of weeks, since these are more specialist tests than routine bloods.

  • Is the histamine and DAO test reliable?

    This is an area of ongoing scientific debate. Blood DAO levels do not always correlate well with gut DAO activity or with symptoms, and there is no single, universally validated test for histamine intolerance. Results should be interpreted cautiously and alongside a detailed symptom and dietary history, ideally with a specialist who understands the current evidence.

  • What happens if my results suggest histamine intolerance?

    Management usually focuses on dietary adjustment under professional guidance, such as a structured low-histamine trial followed by careful reintroduction, rather than relying on the blood test result alone. A doctor or dietitian can help build a plan appropriate to you.

  • How much does private histamine and DAO testing cost?

    Private clinics can arrange this test, often alongside a wider allergy or gut health assessment, with results reviewed by a specialist. Cost varies by provider.

  • Is this test available on the NHS?

    Histamine intolerance is not a formally recognised NHS diagnostic category in the same way as food allergy, so this specific test is not routinely offered on the NHS. Private clinics with an interest in this area are more likely to provide it.

  • How do I book this test privately?

    You can book through a private clinic offering allergy or gastrointestinal testing, typically with an initial consultation to check whether the test is appropriate for your symptoms before proceeding.