Glucose tests are used to determine the concentration of glucose in blood, urine, cerebrospinal fluid, and other body fluids. These tests are used to detect an increased blood glucose (hyperglycemia), a decreased blood glucose (hypoglycemia), increased glucose in the urine (glycosuria), and a decrease in cerebrospinal, serous, and synovial fluid glucose.
Purpose
Glucose tests are used in a variety of situations including:
Screening persons for diabetes mellitus. The American Diabetes Association (ADA) recommends that a fasting plasma glucose (fasting blood sugar) be used to diagnose diabetes. People without symptoms of diabetes should be tested when they are 45 years old and again every three years. People in high-risk groups should be tested before the age of 45 and tested more frequently. 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.
Screening for gestational diabetes. Diabetes that occurs during pregnancy is called gestational diabetes. This condition is associated with hypertension, increased birth weight, and a higher risk for preeclampsia. Women who are at risk are screened when they are 24-28 weeks pregnant. A woman is considered at risk if she is older than 25 years, is not at her normal body weight, has a parent or sibling with diabetes, or is in an ethnic group that has a high rate of diabetes (Hispanic, Native American, Asian, African-American).
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 at or near normal decreased their risk of complications by 50-75%. 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 associated with neuroglycopenia produces symptoms such as confusion, memory loss, and seizure. Demonstration that such symptoms are the result of hypoglycemia requires evidence of a 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 post-prandial causes.
Analysis of glucose in body fluids. High levels of glucose in body fluids reflect a hyperglycemic state and is otherwise not clinically significant. However, low body fluid glucose levels indicate increased glucose utilization which is often caused by infection (e.g., meningitis causes a low CSF glucose); inflammatory disease(e.g., rheumatoid arthritis causes a low pleural fluid glucose); or malignancy (e.g., a leukemia or lymphoma such as Hodgkin's disease infiltrating the central nervous system or serous cavity).
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