Blood Glucose

Fasting blood sugar (FBS)

For a fasting blood sugar test, do not eat or drink anything other than water for at least 8 hours before the blood sample is taken.

If you have diabetes, you may be asked to wait until you have had your blood tested before taking your morning dose of insulin or diabetes medicine.

2-hour postprandial blood sugar

For a Reference 2-hour postprandial test Opens New Window, start eating a meal exactly 2 hours before the blood sample is taken. A Reference home blood sugar test Opens New Window is the most common way to check 2-hour postprandial blood sugar levels.

Random blood sugar (RBS) and glycohemoglobin A1c

No special preparation is required before having a random blood sugar or A1c test.

Oral glucose tolerance test

For an oral glucose tolerance test, you'll need to follow a special diet for 3 days before the test. And do not eat, drink, smoke, or exercise strenuously for at least 8 hours before your first blood sample is taken.

To learn more about how to prepare for this test, see Reference Oral Glucose Tolerance Test.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean.

To help you understand the importance of this test, fill out the medical test information form (What is a Reference PDF Opens New Window document?).

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