Fasting blood sugar test is done to diagnose diabetes. The usual duration of fasting is 8-10 hours but it should not be less than 6 hours. Fating or over fasting in a person who does not have diabetes stimulate the pancreas to secrete a hormone called glucagon, it stimulate the liver to release the sugar blood. Due to this body produces insulin and prevent high blood sugar. If a person has diabetes, the fasting will not affect the blood sugar levels. So, this is the reasons you lab asked to have fasting of 8-10 hours.
