Your fasting blood glucose level is the amount of glucose, or sugar, circulating in your blood after an 8-hour fast. The actual level is determined by a blood test. Abnormal fasting blood glucose levels usually indicate a problem with glucose metabolism, such as hyperglycemia or diabetes. If abnormal levels are detected, further blood testing usually follows an initial fasting blood glucose test to confirm the result.
Method
Fasting blood glucose level is determined by means of a blood test taken after at least 8 hours without anything to eat or drink, except water. The test is called a fasting blood glucose or fasting plasma glucose test. At a doctor's office or lab, blood is taken from a vein in the inner crease of the elbow or the top of the hand.
Purpose
Abnormal fasting blood glucose levels indicate a medical condition such as hypoglycemia, hyperglycemia, diabetes, pre-diabetes or insulin resistance for the purpose of diagnosis or monitoring. Pre-diabetes or insulin resistance may be diagnosed when fasting blood glucose levels are higher than normal but not high enough to be diabetes. Testing may be done twice to confirm the results.
Pre-diabetic conditions are regularly monitored with blood tests because they can turn into type-2 diabetes. People who have diabetes routinely check their fasting and non-fasting blood glucose levels at different times of the day as a way of monitoring their disease and making sure their diet and medication routines are working.
Significance
A fasting blood glucose level of 99 mg/dL or less is normal. A level in the range of 100 to 125 indicates pre-diabetes, or impaired fasting glucose. A level of 126 or higher on second testing indicates diabetes. Other conditions that may result from high blood glucose levels include hyperthyroidism, Cushing syndrome, chronic renal failure, pancreatitis and pancreatic cancer.
Time Frame
The Centers for Disease Control and Prevention recommends everyone 45 years or older be tested for diabetes, especially those who are overweight. Anyone who is younger than 45 and is overweight with at least one other risk factor associated with diabetes, such as a family history, high blood pressure or blood fats, should also be tested.
Considerations
A fasting blood glucose is often the first step in a series of blood glucose tests performed for the purpose of diagnosing diabetes. The most common is an oral glucose tolerance test, or OGTT. After a fasting blood glucose test, the patient drinks glucose and one or more glucose tests are performed to track glucose levels over several hours.
