Glucose Tolerance Test Preparation: What to Know

The test checks how your body handles a measured glucose drink. It is often arranged during pregnancy to look for gestational diabetes, but your clinician may recommend it for other reasons. The exact instructions from the testing clinic take priority because timing and fasting requirements can vary.

You may be asked not to eat for a set period before arriving. Ask whether plain water is allowed and avoid changing the instruction by having juice, milk, tea or coffee. Do not deliberately eat extra sweets beforehand; follow your usual meals until the fasting period begins unless your clinician gives different advice.

Tell the clinic about pregnancy symptoms, diabetes, vomiting, recent illness and every medicine or supplement you use. Some medicines can affect glucose readings, so do not stop or delay a prescribed treatment unless the clinician who ordered it tells you to.

Book a morning appointment if that suits the clinic and your fasting instructions. Bring water if permitted, a snack for after the final blood sample, and something quiet to read because you may need to rest at the clinic between samples. Wear clothing with a sleeve that can be raised comfortably.

During the test, you will usually have a blood sample, drink the glucose solution, and wait for further samples according to the clinic's schedule. Staying seated, avoiding food and following staff instructions help prevent changes that could affect the result. If you vomit or feel unable to finish the drink, tell staff immediately.

Contact the testing clinic before the appointment if you cannot fast, have been vomiting, feel unwell, or are unsure about a medicine instruction. The team can tell you whether to reschedule or adjust the plan.

Tell clinic staff promptly if you develop shaking, sweating, dizziness, weakness, nausea, blurred vision or feel faint during the test. Sit or lie down as directed. Seek urgent medical help for severe fainting, confusion, trouble breathing or symptoms that do not improve after staff assistance.

Ask: How long should I fast? May I drink plain water? Should I take my morning medicines? What should I do if I vomit or cannot complete the drink? When and how will I receive the result?