Oral Glucose Tolerance Test

Assesses how the body responds to a standard glucose load.

To test for impaired glucose tolerance and diabetes, including gestational diabetes, using the appropriate protocol.

1. For several days before the test, keep to your usual diet and physical activity.
2. Come for the test after fasting for the time your doctor has specified.
3. Drink the glucose solution only when instructed by staff.
4. Stay on site until the test is finished and keep to all blood draw times.

Fasting is required, usually for 8–14 hours, according to the specific protocol. For several days beforehand, keep to your usual diet and physical activity unless your doctor tells you otherwise.

It is best to start in the morning: the test lasts several hours, and the exact blood draw times are set by the protocol.

• Sharply restricting carbohydrates in the preceding days
• Walking, smoking or eating during the test
• Errors in the glucose dose or collection times

Venous blood — at several time points

The first sample is taken while fasting. The patient then drinks the prescribed glucose solution, and additional blood samples are taken at set times. During the test you usually need to stay on site, rest and avoid food and physical exertion.

The result is assessed using fasting glucose and glucose at the relevant time points after the load; cutoffs differ in pregnancy protocols.

If you develop severe nausea, dizziness or weakness during the test, tell staff immediately; once you have the result, see your doctor.

The OGTT dose, collection times and diagnostic cutoffs differ for pregnant and non-pregnant patients.