Blood Sugar Tests Health Article

Definition

Blood sugar or plasma glucose tests are used to determine the concentration of glucose in blood. These tests are used to detect an increased blood glucose (hyperglycemia) or a decreased blood glucose (hypoglycemia).

Purpose

Blood glucose tests are used in a variety of situations, including the following:

• Screening persons for diabetes mellitus: The American Diabetes Association (ADA) recommends that a fasting plasma glucose (fasting blood sugar) be used to diagnose diabetes. If the person already has symptoms of diabetes, a blood glucose test without fasting, called a casual plasma glucose test, may be performed. In difficult diagnostic cases, a glucose challenge test called a two-hour oral glucose tolerance test is recommended. If the result of any of these three tests is abnormal, it must be confirmed with a second test performed on another day. The same test or a different test can be used, but the result of the second test must be abnormal as well in order to establish a diagnosis of diabetes.
• Blood glucose monitoring: Daily measurement of whole blood glucose identifies diabetics who require intervention to maintain their blood glucose within an acceptable range as determined by their physician. The Diabetes Control and Complications Trial (DCCT) demonstrated that persons with diabetes who maintained blood glucose and glycated hemoglobin (hemoglobin with glucose bound to it) at or near normal decreased their risk of complications by 50 to 75 percent. Based on results of this study, the American Diabetes Association (ADA) recommends routine glycated hemoglobin testing to measure long-term control of blood sugar.
• Diagnosis and differentiation of hypoglycemia: Low blood glucose may be associated with symptoms such as confusion, memory loss, and seizure. Demonstration that such symptoms are the result of hypoglycemia requires evidence of low blood glucose at the time of symptoms and reversal of the symptoms by glucose. In documented hypoglycemia, blood glucose tests are used along with measurements of insulin and C-peptide (a fragment of proinsulin) to differentiate between fasting and postprandial (after a meal) causes.

Description

The body uses glucose to produce the majority of the energy it needs to function. Glucose is absorbed from the gastrointestinal tract directly and is also derived from digestion of other dietary carbohydrates. It is also produced inside cells by the processes of glycogen breakdown (glycogenolysis) and reverse glycolysis (gluconeogenesis). Insulin is made by the pancreas and facilitates the movement of glucose from the blood and extracellular fluids into the cells. Insulin also promotes cellular production of lipids and glycogen and opposes the action of glucagons, which increases the formation of glucose by cells.

Diabetes may result from a lack of insulin or a subnormal response to insulin. There are three forms of diabetes: Type I or insulin dependent (IDDM), type II or noninsulin dependent (NIDDM), and gestational diabetes (GDM). Type I diabetes usually occurs in childhood and is associated with low or absent blood insulin and production of ketones even in the absence of stressed metabolic conditions. It is caused by autoantibodies to the islet cells in the pancreas that produce insulin, and persons must be given insulin to control blood glucose and prevent ketosis. Type II accounts for 85 percent or more of persons with diabetes. It usually occurs after age 40 and is usually associated with obesity. Persons who have a deficiency of insulin may require insulin to maintain glucose, but those who have a poor response to insulin may not. Ketosis does not develop under normal metabolic conditions but may occur with stress. Gestational diabetes is a form of glucose intolerance that first appears during pregnancy. It usually ends after delivery, but over a 10-year span approximately 30 to 40 percent of females with gestational diabetes go on to develop noninsulin dependent diabetes.

There are a variety of ways to measure a person's blood glucose.

Whole blood glucose tests

Whole blood glucose testing can be performed by a person in his or her home, or by a member of the healthcare team outside the laboratory. The test is usually performed using a drop of whole blood obtained by finger puncture. Care must be taken to wipe away the first drop of blood because this is diluted with tissue fluid. The second drop is applied to the dry reagent test strip or device.