What happens before a glucose tolerance test?

The test checks how your body handles glucose over time. Preparation may involve fasting for a specified period, while still allowing plain water if your clinic says this is permitted. Your clinician may ask about diabetes, pregnancy, recent illness, and medicines or supplements that can affect the result.

After the first sample, the glucose drink is taken according to the clinic’s instructions. Further blood samples are collected at planned times, so the visit can take longer than a routine blood test. Tell staff if the drink causes nausea, sweating, light-headedness, or discomfort.

Follow the written fasting instructions exactly and do not change prescribed medicines unless the requesting clinician tells you to. Arrange enough time to remain at the clinic, bring water if allowed, and take something to eat for after the final sample. Avoid strenuous activity during the testing period because movement can influence glucose handling.

If you are pregnant, mention any vomiting, faintness, or difficulty fasting before the appointment. The team can explain whether another plan is needed.

Contact the clinic before attending if you cannot fast, have been unwell, or have vomited during a previous glucose test. During the appointment, alert staff promptly for fainting, severe weakness, repeated vomiting, breathing difficulty, or swelling. These symptoms need assessment rather than being ignored as routine test effects.

Ask when to stop eating and drinking, whether your regular medicines should be taken, how long the appointment may last, and what happens if you vomit the glucose drink. You can also ask when and how the result will be shared.