Glucose tolerance test, 2 hour glucose

For the sample taken two hours after a 75 g glucose drink; UK laboratories commonly print an upper limit of 7.8 mmol/L. Ranges used in pregnancy differ; use the range printed by the lab.

An oral glucose tolerance test measures how the body handles a set amount of sugar. After an overnight fast, a glucose sample is taken, then a drink containing 75 g of glucose is swallowed and a second sample is taken two hours later. This entry is that two hour value; it shows how quickly the body has brought the sugar back down.

Doctors request it when fasting glucose or HbA1c have not given a clear picture of how the body handles sugar, when looking into sugar handling in pregnancy, and occasionally when looking into low blood sugar after meals.

• Diabetes and pre-diabetes
• Pregnancy, in some women
• Being overweight and insulin resistance
• Steroid medicines
• Not having eaten normally in the days before the test, which makes the body handle sugar less well
• Staying still during the test, compared with walking about

• A normal, quick insulin response
• Walking about during the two hours
• Some diabetes medicines
• Previous stomach surgery, which can cause an early peak and then a low figure at two hours

• Eating a very low carbohydrate diet in the days before makes the two hour figure read higher
• Not fasting properly, or being sick after the drink, invalidates the test
• The result varies from day to day in the same person more than most blood tests

Fast overnight, eat normally in the three days before, and stay seated and do not smoke during the test. The two hour value is read together with the fasting value taken at the start.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.