In a healthy person, the pancreas reacts to the higher blood glucose by releasing insulin, a hormone that converts blood sugar into usable energy.
In addition to carbohydrates, other body processes also raise blood sugar levels.When a person fasts, which is defined medically as not eating or drinking anything aside from water for at least eight hours, the release of glucagon is triggered in the body. Glucagon instructs the liver to metabolize reserve supplies of glycogen, which are then circulated into the bloodstream as sugars. Accordingly, the amount of plasma glucose goes up. This is how the body creates energy even while fasting.
In sum, when diabetes is not present the body responds to all blood sugars by manufacturing insulin in proportion with the glucose level. When it comes to fasting blood sugars, insulin lowers and stabilizes the levels so that they remain in a normal, healthy range. Yet when any form of diabetes is present, either pre-diabetes, Type 1 diabetes or Type 2 diabetes, the whole physiological process doesn’t work correctly, and blood sugars are often considerably higher than normal. The fasting blood sugar test (FBS) is commonly used to detect the existence of diabetes.
In order to prepare for a fasting blood sugar test, one must refrain from eating or drinking from eight to twelve hours before the test, depending upon the doctor’s instructions. It is conducted in the same manner as any laboratory blood test. The health professional will wrap an elastic band around the upper arm in order to restrict blood flow, which enlarges the veins and facilitates the insertion of a needle. After disinfecting the site with alcohol, a needle is placed into the vein and blood is drawn into a vial, which will be then be sent for laboratory testing.
A normal result for fasting blood glucose ranges from 70 – 100 mg/dL. According to criteria set by the American Diabetes Association, a higher than normal fasting blood sugar between 100 to 125 mg/dL (5.6 to 6.9 mmol/L) may indicate prediabetes. This shows an increased risk of developing Type 2 diabetes.
When the measurement is above 126 mg/dL (7 mmol/L), a diagnosis of diabetes is likely. A lower than normal result may point to hypoglycemia that is caused by a specific type of tumor in the pancreas, and further diagnostic testing is needed.
Besides eating or drinking during the eight hours before the fasting blood sugar test, other factors may influence the outcome. Illness, drinking alcohol or excessive caffeine the day before, smoking and emotional stress can all impact blood sugar levels. Fasting blood sugar tests should therefore be performed twice, on two separate days, in order to confirm that results are consistent.