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Oral glucose tolerance test (OGTT): Prolonged five hour test with insulin

Patient information A-Z

Your doctor has referred you for an oral glucose tolerance test (OGTT) to assess the amount of insulin and/or C-peptide that you produce. This test can be used to investigate reactive hypoglycaemia.

You will receive a separate appointment letter for this test. The timing of the test is important, so please attend at the time specified on your appointment letter. If you are unable to attend your appointment please contact the Endocrine Unit on the number below to rearrange it.

About the test

Do I need to prepare for the test?

You will need to fast from midnight the night before your test. Only plain water can be drunk during the fasting period and the test. If you have diabetes please let us know before you attend for the test.

What happens during the test?

You will need to arrive at the Endocrine Investigation Unit by 09:00. A fine plastic tube, called a cannula, will be inserted into a vein in your arm to allow us to take blood samples at regular intervals. After a short resting period and the first blood test, you will be given a glucose drink or the equivalent of a mixed meal. Blood samples will be taken to measure insulin and/or C-peptide at regular intervals. We will also be checking your blood sugar levels. During the test you are not allowed anything to eat and only plain water to drink.

How long will the test take?

You will be in the Endocrine Investigation Unit for at least five hours. You may wish to bring a book or magazine to read as well as something to eat at the end of the test.

Will I experience any side effects?

Occasionally, some people experience nausea and headaches during the test; these usually resolve within a short time.

When will I get my results?

Results cannot be given out over the telephone; they will be discussed with you at your next clinic appointment.

General information

Discounted parking is available for patients attending clinic appointments over three hours duration. Please present your appointment letter to receive this.

Food and drink: there is a coffee shop in the treatment centre atrium and further food and drink facilities in the main hospital concourse.

If you have any further questions, please contact the Endocrine Unit on 01223 217848.

We are smoke-free

Smoking is not allowed anywhere on the hospital campus. For advice and support in quitting, contact your GP or the free NHS stop smoking helpline on 0800 169 0 169.

Other formats

Help accessing this information in other formats is available. To find out more about the services we provide, please visit our patient information help page (see link below) or telephone 01223 256998.

Contact us

Cambridge University Hospitals
NHS Foundation Trust
Hills Road, Cambridge

Telephone +44 (0)1223 245151