--- title: "Fasting before a blood test: What to Expect | HealthAnswers" description: "Which blood tests may require fasting, whether water and medicines are allowed, and why the test provider" url: https://healthanswers.co.uk/tests/fasting-before-blood-tests/ robots: noindex --- # Fasting before a blood test: What to Expect | HealthAnswers Tests & investigations Which blood tests may require fasting, whether water and medicines are allowed, and why the test provider's instructions take priority. Written by HealthAnswers editorial team Medical review not recorded. Updated and source-checked with AI assistance. Sources checked 8 September 2026 ## Quick answer Do I need to fast before my blood test? Most blood tests do not require fasting. When fasting is requested, it often means no food and only plain water for a specified number of hours. Ask the arranging clinician about medicines before fasting. If you use insulin or other diabetes medicines, get an individual plan rather than following generic fasting instructions. ## Who is this page for? This page is for people in the UK who want a plain-English overview of Fasting before a blood test, including when to seek help and what NHS care usually involves. It explains general information, not what is wrong with you personally. ## Who should skip this page? Skip this page if you need a diagnosis, a prescription, or emergency care. It cannot replace a GP, pharmacist, NHS 111 or 999. If you are in immediate danger, call 999; for urgent advice that is not life-threatening, call 111 in England, Scotland or Wales, or use your GP out-of-hours service in Northern Ireland. On this page 5 sections ## Key facts about the fasting before a blood test - Follow the instructions from the service that ordered the test. - Plain water is usually encouraged unless specifically restricted. - Never change insulin or other medicine without an agreed plan. ## Tests that may use fasting Fasting is sometimes requested for glucose, triglyceride or specialist metabolic tests. Requirements vary, so generic internet instructions should not replace the laboratory’s directions. ## During the fast Use only plain water when allowed. Avoid tea, coffee, chewing gum, sweets, smoking and vigorous exercise unless the service says otherwise. ## Diabetes and other health needs Fasting can cause low glucose when using insulin or certain tablets. Obtain a clear plan for medicine, monitoring, appointment timing and what to bring for afterwards. ## What should I confirm before the appointment? Check the exact test, when to stop eating, what you can drink, and whether the appointment should be in the morning. Ask how to manage a medicine that must be taken with food. [East Kent Hospitals’ patient leaflet](https://leaflets.ekhuft.nhs.uk/fasting-for-your-blood-test/html/) illustrates why preparation needs to match the instructions from your own service. If your booking message and the printed leaflet differ, contact the service to clarify them. Do not extend a fast because an internet page gives a different number of hours. ## What if I accidentally eat or drink? Tell the person taking your blood exactly what you had and when. They can check whether to proceed or rearrange; do not conceal it or decide that the result will be unaffected. If fasting makes you unwell, seek appropriate help and contact the service about a safer plan. Before leaving, ask when the result is expected and who will explain it. Our guide to [getting your NHS test results](https://healthanswers.co.uk/guides/getting-nhs-test-results/) helps you keep track of the follow-up. ## ! When to speak to a doctor about the fasting before a blood test Contact the test provider before the appointment if instructions are unclear, you have diabetes, are pregnant, have a history of fainting, or fasting may be unsafe. Tell the phlebotomist if you ate, drank something other than water or changed medicine—the test may still be useful or can be rearranged. ## Common questions about the fasting before a blood test Can I drink water while fasting? Plain water is usually allowed and can make blood collection easier, unless your service specifically says otherwise. Can I take my morning medicines? Often yes, but some tests and diabetes medicines need specific instructions. Confirm with the requesting service. Does a cholesterol test require fasting? Many cholesterol tests are now non-fasting, but some lipid or triglyceride assessments may use fasting. Follow your invitation. ## Sources - [East Kent Hospitals — Fasting for your blood test](https://leaflets.ekhuft.nhs.uk/fasting-for-your-blood-test/html/) - [NHS — Blood tests](https://www.nhs.uk/tests-and-treatments/blood-tests/)