Your doctor may examine how well your body breaks down glucose, which is used for energy, if she suspects you have diabetes. As part of the test, you will consume oral glucose. Tests that show a high level of glucose in your blood after an hour or two indicate a problem. Insulin helps your body utilize glucose for energy. With diabetes, you have high blood glucose levels either because your body does not use insulin correctly or because your body does not produce enough insulin, according to the Centers for Disease Control.
Time Frame
Your health care provider will provide the oral glucose that is used to screen for diabetes. During the test, called the oral glucose tolerance test, you are given a liquid that contains glucose. Health care providers will take your blood prior to consuming the oral glucose, then every 30 to 60 minutes following the time you drink it. Your test can take up to three hours. You cannot eat or drink anything for eight to 10 hours prior to the test.
Significance
If you show abnormal blood-glucose levels after taking oral glucose you may have type 2 diabetes. However, high glucose levels also can indicate other problems, so it's important to have your doctor evaluate your test results, according to Drugs.com.
Function
Normal results would be 60 to 100 mg per deciliter of blood after fasting; less than 200mg/dL at the one hour point; and less than 140 mg/dL at the two hour point. If your results show a blood glucose level between 140 and 200mg/dL, you have impaired glucose tolerance, which is sometimes called "pre-diabetes," according to NIH. If the results show your level is higher than 200mg/dL you likely have diabetes.
Oral glucose tolerance tests also are used to screen for gestational diabetes. This test is given between the 24th and 28th week of pregnancy. Normal blood values for a 50g oral glucose tolerance test are 140mg/dL at the one hour point, according to NIH. If you are given a 100g oral glucose tolerance test, normal values are: 95mg/dL for fasting; 180mg/dL or less at one hour; 155mg/dL or less at two hours; and 140mg/dL or less at three hours, according to NIH.
Considerations
Some people cannot absorb oral glucose. If you have a malapsorption disorder or short bowel syndrome you may be among them. If this is the case, you need an intravenous glucose tolerance test to screen for diabetes, according to Lippincott Williams and Wilkins' book, "Lippincott's Nursing Procedures."
Potential
Oral glucose also may be used to reverse hypoglycemia that is caused by too much insulin, says R.A. Heptulla, author of a study published in the "Journal of Clinical Endocrinology and Metabolism." Oral glucose works by affecting your hormone response during insulin-induced hypoglycemia, or blood sugar that is too low due to too much insulin.
References
- National Institutes of Health: Glucose Tolerance Test
- Drugs.com: Glucose Tolerance Test
- "Lippincott's Nursing Procedures"; Lippincott Williams and Wilkins; 2008
- Centers for Disease Control: Oral Glucose Tolerance Test (OGTT) Procedures Manual
- PubMed: "Journal of Clinical Endocrinology and Metabolism"; Oral glucose augments the counterregulatory hormone response during insulin-induced hypoglycemia in humans; R.A. Heptulla et al.; 2001
- National Diabetes Information Clearinghouse: Insulin Resistance and Pre-Diabetes
