Fasting Blood Glucose (FBG) Test

What happens if I accidentally eat before the test?

Let the lab staff know immediately — eating can raise your glucose reading significantly, and the test will likely need to be repeated after a proper fast for an accurate result.

Can I drink water while fasting for this test?

Yes, plain water is allowed and actually encouraged during the fasting period; it's food, sugary drinks, coffee, and tea that need to be avoided.

Is one high fasting glucose reading enough to diagnose diabetes?

Usually not — most guidelines recommend confirming an elevated result with a repeat test on a different day, or with an HbA1c test, before making a formal diabetes diagnosis.

How is this different from a random glucose test?

A random glucose test can be taken at any time regardless of your last meal, while fasting glucose specifically requires an 8–12 hour fast beforehand for a more standardized, comparable result.