Glucose Test

Pictures & Images

See all Pictures & Images

Why is the Test Performed?

This test is used to evaluate blood glucose levels. It may be used to diagnose or screen for diabetes and to monitor control in patients who have diabetes.

Most dietary carbohydrate eventually ends up as glucose in the blood. Excess glucose is converted to glycogen for storage by the liver and skeletal muscles after meals. Glycogen is gradually broken down to glucose and released into the blood by the liver between meals. Excess glucose is converted to triglyceride for energy storage.

Glucose is a major source of energy for most cells of the body. Some cells (for example, brain and red blood cells), are almost totally dependent on blood glucose as a source of energy. The brain, in fact, requires that glucose concentrations in the blood remain within a certain range in order to function normally. Concentrations of less than about 30 milligrams per deciliter (mg/dL) or greater than about 300 mg/dL can produce confusion or unconsciousness.

The major hormone regulating glucose concentration in the body is insulin (although other hormones such as glucagon, epinephrine, and cortisol also affect it).

Glucose levels are measured most commonly to diagnose diabetes or to monitor adequacy of diabetic control. Diabetes is a very common disease, affecting about 2% of the general population, that results from insulin deficiency or insensitivity by the body to the level of insulin present. People with type 1 diabetes require daily injections of insulin to control their disease. Injection of too much or too little insulin can be dangerous because there is a limited range of blood sugar levels in which the brain can function normally.