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Two-Hour Postprandial Glucose

Does this test have other names?

Glucose, postprandial; glucose, two-hour postprandial; two-hour PPG; two-hour postprandial blood sugar; O'Sullivan test 

What is this test?

This is a blood test to check for diabetes. If you have diabetes, your body doesn't make enough insulin to keep your blood sugar in check. This means your blood sugar levels are too high, and over time this can lead to serious health problems including nerve and eye damage.

This test is done to see how your body responds to sugar and starch after you eat a meal. As you digest the food in your stomach, blood glucose, or blood sugar, levels rise sharply. In response, your pancreas releases insulin to help move these sugars from the blood into the cells of muscles and other tissues to be used for fuel. Within two hours of eating, your insulin and blood glucose levels should return to normal. If your blood glucose levels remain high, you may have diabetes. 

Why do I need this test?

Your doctor may order this test to see if you have diabetes or another insulin-related disorder, especially if you have symptoms such as:

  • Frequent urination

  • Unusual thirst

  • Blurred vision

  • Tiredness

  • Repeated infections

  • Sores that heal slowly

If you're pregnant, you may have this test to screen for gestational diabetes, the short-term diabetes that can develop during pregnancy. Treating gestational diabetes reduces the risk for health problems for you and your baby. 

What other tests might I have with this test?

Your doctor may order other tests to confirm or evaluate whether you have diabetes. These may include:

  • Fasting blood glucose test. This measures the amount of sugar in your blood.

  • A1C (glycosylated hemoglobin) test. This measures your average blood sugar level over the last two to three months.

  • Glucose tolerance test. This measures your body's ability to use sugar after drinking a standard amount in a sugary drink. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Test results vary by age and are usually measured in milligrams per deciliter (mg/dL). Normal results for the two-hour postprandial test based on age are:

  • Newborn to 50 years: less than 140 mg/dL

  • 50 to 60 years: less than 150 mg/dL

  • 60 years and older: less than 160 mg/dL

A normal result for the one-hour glucose screen for gestational diabetes is less than 140 mg/dL.

If your blood glucose level is still high two hours after you've eaten, or if it is high one hour after a gestational diabetes glucose tolerance test, it could be a sign that you have an insulin-related problem.  

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. A blood sample is taken before you eat, to provide a baseline, and then again two hours after you've eaten.

If you are having the glucose test for gestational diabetes, you will first be given a sugary drink. 

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

Your test results might be affected if you:

  • Smoke during the test period

  • Are under extreme stress

  • Eat a snack or candy after your meal and before you're tested

  • Are unable to eat the entire meal

  • Exercise during the testing period

How do I get ready for this test?

You must fast for 12 hours before the test and then eat a meal high in carbohydrates, such as bread, cereal, rice, or potatoes. This high-carbohydrate meal should have at least 75 grams of carbohydrates. After the meal, don't eat anything else before having the test. Plan to rest during the two-hour waiting period, because exercise can cause blood sugar levels to rise. You may not have to fast if you're pregnant.