Two-hour glucose test

The clinician may take an initial sample, give you a glucose solution, and collect another sample around two hours later. You will usually remain at the testing centre and should avoid eating, smoking or strenuous activity unless instructed otherwise. Temporary nausea or light-headedness can occur after the drink. The result is read alongside your symptoms, examination and other blood work rather than in isolation.

A test may be arranged when a clinician is investigating fatigue, thirst, unusual urination or another concern. Conditions such as [Anaemia](/conditions/anaemia/), [Chronic Kidney Disease](/conditions/chronic-kidney-disease/) and [Coeliac Disease](/conditions/coeliac-disease/) can also affect health and need their own assessment; a glucose test does not diagnose them.

Check whether fasting is required and ask how to take regular medicines on the morning of the appointment. Keep your usual routine unless the clinic says otherwise, and tell staff about pregnancy, recent illness or changes in eating. Bring water only if permitted by the instructions. If you feel shaky, sweaty, sick or faint, tell the staff promptly instead of leaving the site.

After testing, follow the advice about food and activity. Ask when the report will be reviewed and whether another blood test is needed to clarify the finding.

Seek urgent help for confusion, collapse, severe weakness, repeated vomiting or difficulty breathing. Contact your clinician promptly if symptoms of high or low glucose continue after the appointment, or if you are unable to keep fluids down. A result outside the expected range needs planned follow-up, not self-treatment or sudden dietary restriction.

Ask what the test is investigating, whether fasting applies, which medicines may affect the reading, and how the result will be interpreted. If you have ongoing fatigue or digestive symptoms, ask whether [Chronic Fatigue Syndrome](/conditions/chronic-fatigue-syndrome/) or [Crohn's Disease](/conditions/crohns-disease/) needs separate consideration.