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.

Fasting before a blood test: What to Expect

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.

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 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 helps you keep track of the follow-up.

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

How we reviewed this page

Medical review is not recorded for this page.

First published: 1 August 2026
Sources checked: 8 September 2026

Written by HealthAnswers editorial team. Published by HealthAnswers (Elite Digital AI Solutions Ltd). How we review content · Report a problem with this page