An oral glucose tolerance test (OGTT) measures how your child’s body uses sugar (glucose). Glucose is the body’s main source of energy.
The test results can help your care team identify problems with blood sugar levels and diagnose conditions such as prediabetes, diabetes, or reactive hypoglycemia.
How an oral glucose tolerance test works
An oral glucose tolerance test measures your child’s blood sugar levels over time after they drink a liquid glucose solution.
A blood sample is collected from a vein to measure your child’s starting blood sugar level.
Your child drinks a sweet liquid (glucose solution) within a set amount of time.
Additional blood samples are taken over time to see how your child’s blood sugar levels change.
Normally, blood sugar rises after drinking the glucose solution and then returns to normal. If blood sugar stays too high or drops too low, it may be a sign of a problem.
How to prepare for an oral glucose tolerance test
Always follow your care team's instructions for how to prepare your child for the test.
Follow fasting (NPO) guidelines for when your child should stop eating and drinking before the test. Your care team will tell you when your child should begin fasting, usually about 8 hours before the test. At that time, stop giving your child solid food, liquids, and enteral (tube) feeds. Your child can continue to drink water.
Talk to your care team about your child’s medicines. Give your child their usual medicines the day of the test unless your care team tells you otherwise.
Have your child wear comfortable clothes.
Bring activities such as books, games, or a tablet that your child can use during the test.
What to expect during the test
Your care team will explain what to expect during your child's test. In general, for this test:
You will stay with your child during the test.
Before the test, your = care team will place an IV in your child’s arm to use for blood samples.
The care team will give your child a sweet liquid (glucose solution) to drink over 5 minutes.
Blood samples will be collected at set times during the test, often every 30 minutes for 2 hours or longer, depending on the reason for testing.
A nurse will monitor your child during the test.
At the end of the test, the IV will be removed.
The test usually takes about 3-4 hours.
Possible side effects of an oral glucose tolerance test
The test is generally safe. Some children may have minor side effects from the sugary drink or the needle stick for the IV. Possible side effects include:
Mild nausea after drinking the glucose solution
Feeling dizzy or lightheaded
Pain or discomfort from the needle stick
Mild bruising at the IV site
Feeling shaky or tired
Side effects are usually temporary and improve shortly after the test.
After the oral glucose tolerance test
Your child can usually resume normal eating and return to normal activities after the test.
Blood samples will be sent to a lab for testing. Your care team will let you know when to expect the test results and explain the results to you when they are ready.
What test results mean
Based on your child’s blood sugar levels, your child’s results may show one of the following:
Normal: Blood sugar levels rise and then return to normal after a few hours.
Prediabetes: Blood sugar levels rise and are higher than normal, but not high enough to be called diabetes (high blood sugar).
Diabetes: Blood sugar levels rise and stay higher than normal over time.
Reactive hypoglycemia: Blood sugar levels rise and then drop below a normal level.
Based on the test results, your care team will discuss other tests or treatments that may be needed.
Questions to ask your care team
Why does my child need an oral glucose tolerance test?
What is a normal blood sugar level?
How do I prepare my child for the test?
Does my child need to fast before the test?
Can my child take their usual medicines before the test?
How can I keep my child comfortable during the test?
Can my child leave the room during the test?
What side effects should I watch for during or after the test?
What if my child feels sick during the test?
When and how will we get the test results?
What treatments may be needed based on the test results?
Key points about an oral glucose tolerance test
An oral glucose tolerance test (OGTT) shows how the body uses glucose (sugar).
Your child will drink a sweet liquid (glucose solution) during the test.
Blood samples are collected to measure changes in blood sugar levels over time.
The test can help diagnose problems with your child’s blood sugar levels.
Most children can return to normal activities after the test.
