The oral glucose tolerance test (OGTT) is used to evaluate abnormal fasting blood glucose for diagnosis of diabetes mellitus.
Patients should be in a fasting state (having no food or drink except water for at least 10 hours), prior to the test. This ensures that the blood sugars are not falsely elevated during the test.
Before the test begins, a blood sample will be taken to assess baseline values. Typically, the baseline is a fasting blood glucose.
Normal values at baseline should be less than 100 mg/dL.
Blood samples will be taken 30 minutes after glucose ingestion, and again at 60 minutes.
Normal values 30 and 60 minutes after glucose ingestion are below 200 mg/dL.
The last set of glucose samples are drawn 120 minutes (2 hours) after baseline.
Levels greater than 140 mg/dL indicate impaired glucose tolerance, with values greater than 200 mg/mL at the 120 minute mark are diagnostic for diabetes mellitus.
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