The fasting blood glucose test is part of most regular medical checkups and your doctor may also order one if she suspects you have hypoglycemia or diabetes. If your fasting glucose is between 50 and 100 mmol/L, you have normal glucose. If your fasting glucose is between 100 and 125 mmol/L, you have impaired glucose tolerance. Fasting glucose of 126 mmol/L and above indicates diabetes and below 50 mmol/L indicates a hypoglycemic blood glucose.
Reason for Fasting
The most accurate picture of your body's handling of glucose is when your body has fully processed any food or glucose-altering substances and is essentially at rest. Even glucose tolerance tests -- for which you consume a precise amount of glucose and your doctor measures your body's response -- are administered after you have done an eight- to 12-hour fast. Although you are permitted to eat dinner the night before your fasting glucose test, try to finish eating a minimum of eight hours before the scheduled time for the test.
Coffee
Coffee contains several compounds that can affect glucose metabolism, including caffeine, chlorogenic acid and magnesium. Because of the potential impact to the outcome of your fasting plasma glucose test, you should not have coffee or tea after you finish your dinner the night before the test or the morning before your test.
Alcohol
As with most other medical tests, you should not drink alcohol before you take the fasting plasma glucose test. Alcohol impacts your body's insulin levels and, therefore, your glucose levels. Abstain from alcohol for at least 12 hours before your test and preferably 24 hours to ensure that all of the glucose-altering effects of alcohol are out of your system.
Other Activities
In addition to avoiding all food and beverages, except for water, during the eight to 12 hours, you should also refrain from smoking as well as exercise. Make sure that you have completed all of your exercise and other demanding physical activities before you enter the eight to 12 hour pre-test window.
References
- HealthCentral; Screening Tests; July 2006
- "Diabetologia"; Coffee Consumption and Incidence of Impaired Fasting Glucose, Impaired Glucose Tolerance, and Type 2 Diabetes: The Hoorn Study; R.M. van Dam, et al.; 2004
- "Journal of the American Medical Association"; Effects of Moderate Alcohol Intake on Fasting Insulin and Glucose Concentrations and Insulin Sensitivity in Postmenopausal Women: A Randomized Controlled Trial; M.J. Davies, et al.; May 2002
- "Manual of Nursing, Volume 1"; M. E. Vlok; 1992
