Synonyms: GTT; OGTT; Oral Glucose Tolerance Test Why It Is Done The OGTT may be ordered to help diagnose diabetes and as a follow-up test to an elevated blood glucose. Blood glucose testing can be used to screen healthy, asymptomatic individuals for diabetes and pre-diabetes because diabetes is a common disease that begins with few symptoms. It may also be ordered when a patient has a routine physical exam. Screening is especially important for people at high risk of developing diabetes, such as those with a family history of diabetes, those who are overweight, and those who are more than 40 to 45 years old. The glucose test may also be ordered to help diagnose diabetes when someone has symptoms of hyperglycemia, such as: • Increased thirst • Increased urination • Fatigue • Blurred vision • Slow-healing infections or symptoms of hypoglycemia, such as: • Sweating • Hunger • Trembling • Anxiety • Confusion • Blurred Vision Test Overview: Glucose tolerance testing is a series of blood glucose tests. A fasting glucose is collected; then the patient drinks a standard amount of a glucose solution to "challenge" their system. This is followed by one or more additional glucose tests performed at specific intervals to track glucose levels over time. How to prepare for the test    Patient should fast 12-14 hours before collection of specimens.