Fasting Glucose
Fasting glucose tests measure the amount of glucose in the blood when the patient hasn't eaten for several hours (usually a minimum of eight hours without eating or drinking anything except water). The National Institute of Diabetes Digestive and Kidney Disorders (NIDDK) notes that fasting blood glucose tests are the preferred way of screening patients for diabetes because they represent the patient's baseline blood glucose health. Food consumption leads to an elevation of blood glucose--but the increase in blood sugar varies depending on what the food is, as well as how much of it is consumed. Because this can be difficult to account for, fasting blood glucose is the easiest way to see if a patient has diabetes or pre-diabetes.
Sampling
Fasting blood glucose tests require a sample of blood. Lab Tests Online notes that sometimes just a few drops of blood are needed, in which case the patient's finger can be pricked with a lancet (a procedure also known as a finger stick). The small wound can then be squeezed in order to get a few drops of blood for testing. In other situations, the blood sample can be gotten from a vein in the arm. This method is often used if other blood tests are also going to be performed on the patient. Both methods are acceptable, however, for obtaining a sample for fasting blood glucose analysis.
Glucose Measurement
Blood glucose tests use chemicals that react with glucose in the blood. Some blood glucose tests involve exposing a strip of paper coated with chemicals to the blood sample. The chemicals on the paper react with the glucose and change color. The color that they become depends on the concentration of glucose in the blood. Other testing methods use chemicals that generate a small electrical current when they react with glucose. These tests then have a device that measures the electric current and converts the magnitude of this electrical activity to a blood glucose concentration.
