Oral Glucose Tolerance Test (GTT/oGTT)

Patient Experience

  • Reference Number: HEY1426-2024
  • Departments: Renal Service
  • Last Updated: 1 April 2024


This leaflet has been produced to give you general information about your investigation.  Most of your questions should be answered by this leaflet. It is not intended to replace the discussion between you and your doctor, but may act as a starting point for discussion. If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team caring for you.

What is an Oral Glucose Tolerance Test (GTT/oGTT)?

The oral glucose tolerance test (also known as a GTT or oGTT) is used to investigate if you have diabetes by assessing how your body responds to a dose of glucose (sugar) given as a drink.

You have been asked to have GTT as part of post transplantation diabetic screen. GTT is used to investigate if you have diabetes by checking your blood sugar levels before and after having a glucose drink.

The test will last around 3 hours. You will be required to stay in the hospital during that time to provide blood samples.

You should not experience any side effects.

Before the test:

  • You should eat normally for at least 3 days before the test and should not have been dieting.
  • On the day before the test is due, stop eating food by 10:00 pm. You are allowed to drink water but must avoid all other drinks.
  • Do not chew gum or sugar free sweets, and do not smoke or use e-cigarettes or nicotine patches.
  • Other than water, do not have anything to eat or drink on the morning of the test.
  • If you take tablets or medicines, you can take these as usual, except for any medication that needs to be taken with food. You will need to discuss delaying this medication until after the GTT with your doctor

During the test:

  • A blood sample will be taken when you arrive.
  • You will be given a drink containing a known amount of glucose.
  • Once you have finished the glucose drink you will be given a small cup of water.
  • You will be asked to sit for 2 hours, so please bring something to do to keep yourself occupied. You may drink plain water but you must not eat or smoke.
  • A second blood sample will be taken 2 hours after you have finished the drink. You can then eat and drink normally, so do bring a snack in with you.

Please read the information leaflet.  Share the information it contains with your partner and family (if you wish) so that they can be of help and support.  There may be information they need to know, especially if they are taking care of you following this examination.

On the day of your test please attend Outpatient Clinic and report to the reception.

The results will be discussed with you during your next clinic appointment or via telephone.

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with your doctor.  You will be asked to sign a consent form and you should be satisfied that you have received enough information before going ahead. 

Should you require further advice on the issues contained in this leaflet, please do not hesitate to contact the Renal Department on tel: 01482 675050

Further links:

Lab Tests Online UK Website:
This is a free resource created and updated by laboratory

General Advice and Consent

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with the healthcare team.

Consent to treatment

Before any doctor, nurse or therapist examines or treats you, they must seek your consent or permission. In order to make a decision, you need to have information from health professionals about the treatment or investigation which is being offered to you. You should always ask them more questions if you do not understand or if you want more information.

The information you receive should be about your condition, the alternatives available to you, and whether it carries risks as well as the benefits. What is important is that your consent is genuine or valid. That means:

  • you must be able to give your consent
  • you must be given enough information to enable you to make a decision
  • you must be acting under your own free will and not under the strong influence of another person

Information about you

We collect and use your information to provide you with care and treatment. As part of your care, information about you will be shared between members of a healthcare team, some of whom you may not meet. Your information may also be used to help train staff, to check the quality of our care, to manage and plan the health service, and to help with research. Wherever possible we use anonymous data.

We may pass on relevant information to other health organisations that provide you with care. All information is treated as strictly confidential and is not given to anyone who does not need it. If you have any concerns please ask your doctor, or the person caring for you.

Under the General Data Protection Regulation and the Data Protection Act 2018 we are responsible for maintaining the confidentiality of any information we hold about you. For further information visit the following page: Confidential Information about You.

If you or your carer needs information about your health and wellbeing and about your care and treatment in a different format, such as large print, braille or audio, due to disability, impairment or sensory loss, please advise a member of staff and this can be arranged.