The Fasting Blood Sugar Test (also known as the Fasting Plasma Glucose test or FPG) is a blood test that measures the amount of sugar in blood after eight hours or more without food.
This test must be performed by a medical professional.
The FPG is used to diagnose pre diabetes and Type 2 diabetes, as well as
to determine the effectiveness of prescribed treatments for these
conditions. The test, also referred to as a carbohydrate metabolism
test, measures plasma glucose levels after a fast. Fasting, or going
without food for eight hours or more, causes glucagon (a hormone
produced in the pancreas) to release sugar – in the form of glucose –
into the bloodstream.
At this point, people without Type 2 diabetes will produce an adequate amount of insulin to counteract the resulting increase of sugar, which will bring the sugar levels down. People with Type 2 diabetes are unable to do this adequately.
The test does require eight hours of fasting before the test is administered and must be given by a medical professional. Since fasting is required, most doctors prefer administering this test first thing in the morning, before breakfast is eaten. Another reason doctors prefer earlier tests is that morning readings tend to be higher than afternoon readings. While an afternoon read could potentially mask a pre diabetes diagnosis, a morning FPG test is more apt to detect sugar levels that warrant intervention.
For good measure, the test is generally given twice for diagnosing pre diabetes and/or diabetes, but may be ordered throughout your treatment cycle in order to determine the effectiveness of medications and/or lifestyle changes for controlling sugar levels in the blood.