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Blood test

G6PD test

G6PD 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: the activity of glucose-6-phosphate dehydrogenase, an enzyme that protects red blood cells from oxidative damage.

  • Why it is ordered: before prescribing medicines that can trigger haemolysis - such as some antimalarials - and after unexplained episodes of red cell breakdown.

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

  • Reference ranges: testing during or just after a haemolytic episode can read falsely normal, because the most deficient cells have already been destroyed. Every laboratory publishes its own interval, so the range printed on your report is the one that applies to you.

  • A raised result or normal activity is reassuring and clears the medicines in question. A low result or deficient activity means certain drugs, fava beans and some infections can trigger sudden haemolysis, and you should carry a list of what to avoid.

  • 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 G6PD test measures the activity of glucose-6-phosphate dehydrogenase, an enzyme that protects red blood cells from oxidative damage. Doctors most often request it before prescribing medicines that can trigger haemolysis - such as some antimalarials - and after unexplained episodes of red cell breakdown. No fasting or special preparation is needed for this test on its own. Testing during or just after a haemolytic episode can read falsely normal, because the most deficient cells have already been destroyed, 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 or normal activity is reassuring and clears the medicines in question, while a low result or deficient activity means certain drugs, fava beans and some infections can trigger sudden haemolysis, and you should carry a list of what to avoid, 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 G6PD test can usually be booked within days - through a private GP, a walk-in phlebotomy clinic or a self-request home-testing service - and it is most relevant for people with family origins in Africa, the Mediterranean, the Middle East and South and South-East Asia. 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 G6PD test.

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

  • What is a G6PD test?

    This blood test measures the activity of glucose-6-phosphate dehydrogenase, an enzyme that helps protect red blood cells from damage. A deficiency in this enzyme can make red blood cells vulnerable to breaking down under certain triggers, a condition called G6PD deficiency.

  • Why would a doctor order a G6PD test?

    It's often requested when someone has had unexplained episodes of jaundice or anaemia, particularly after certain infections, foods like fava beans, or medications. It's also relevant before prescribing certain drugs known to trigger reactions in people with the deficiency, and is more common in people of Mediterranean, African, and Asian heritage.

  • Do I need to prepare for it?

    No special preparation is usually needed, though it's best avoided during or shortly after an acute episode of red cell breakdown, as this can affect accuracy. Your doctor will advise on the best timing if this applies to you.

  • What happens during the test?

    It's a straightforward blood sample taken from a vein in your arm, similar to any routine blood test.

  • Does it hurt or have risks?

    Only the usual minor discomfort of a blood draw, with no significant risks.

  • How long do results take?

    Results typically take a few days, as this isn't always a same-day laboratory test.

  • What do abnormal results mean, and what happens next?

    A confirmed deficiency means certain medications, foods, and infections should be avoided or approached with caution to prevent a reaction. Your doctor will provide guidance on what to avoid and may give you information to share with future healthcare providers or pharmacists.

  • How much does it cost privately, and is it available on the NHS?

    G6PD testing is available on the NHS, particularly for newborn screening in some cases or when clinically indicated. Private testing can be arranged quickly with specialist interpretation, cost varying by provider.

  • Is it accurate and reliable?

    The test is generally reliable, though results can be temporarily normal during an active episode of red cell breakdown, which is why timing matters. Your doctor will consider this when deciding whether or when to test.

  • How do I book it privately, and how quickly can I be seen?

    You can book a private blood test, with results and specialist guidance usually available within a few days.