For this test, you'll be asked not to eat for a minimum of 8 hours prior to the test. For this reason, many people prefer to do it first thing in the morning after they've fasted all night while sleeping. Fasting up to 12 hours is permitted.
People with diabetes have high blood glucose levels and may show signs of hyperglycemia (note: diabetes is not the only reason for high blood glucose levels, but it is one of the most common).
If you have been showing signs of diabetes, you should discuss them with your doctor as soon as possible. A diabetes blood test can end the uncertainty. If the test results suggest that you have the disease, your doctor will repeat the test at a different time to confirm that you have diabetes. Another test called the A1C test may also be recommended by your doctor. This test measures the average blood sugar levels over a 3-month period. This test, as well as others, may also be done to determine whether you have Type 1 or Type 2 diabetes.