Glucose is the major carbohydrate present in the peripheral blood. Oxidation of glucose is the major source of cellular energy in the body. Glucose derived from dietary sources is converted to glycogen for storage in the liver or to fatty acids for storage in adipose tissue. The concentration of glucose in blood is controlled within narrow limits by many hormones, the most important of which are produced by the pancreas.
The most frequent cause of hyperglycemia is diabetes mellitus resulting from a deficiency in insulin secretion or action. A number of secondary factors also contribute to elevated blood glucose levels. These include pancreatitis, thyroid dysfunction, renal failure, and liver disease.
Hypoglycemia is less frequently observed. A variety of conditions may cause low blood glucose levels such as insulinoma, hypopituitarism, or insulin induced hypoglycemia. Glucose measurement in urine is used as a diabetes screening procedure and to aid in the evaluation of glucosuria, to detect renal tubular defects, and in the management of diabetes mellitus. Glucose measurement in cerebrospinal fluid is used for evaluation of meningitis, neoplastic involvement of meninges, and other neurological disorders.
The measurement and interpretation of glucose concentrations is an area of much confusion. Plasma glucose is about 12% greater than that of whole blood because plasma has a higher water content as it contains no red blood cells. In the fasting state there is little difference between arterial, capillary and venous glucose concentrations but after carbohydrate intake glucose concentration in arterial and capillary samples can exceed those of venous samples by as much as 1.8 mmol/l. This is of particular practical importance in the interpretation of oral glucose tolerance tests.
For the measurement of glucose a specimen containing sodium fluoride to inhibit glycolysis and stabilise the glucose concentration is preferred. If blood is collected into a tube without preservative, glucose concentration can decrease by as much as 7% each hour as a result of glycolysis. Clinically significant decreases in glucose concentration have been reported even with use of preservative. If a tube without preservative is used and delay in transit to the laboratory is anticipated, storage at 4oC is preferable.
Glucose is the major carbohydrate present in the peripheral blood. Oxidation of glucose is the major source of cellular energy in the body. Glucose derived from dietary sources is converted to glycogen for storage in the liver or to fatty acids for storage in adipose tissue. The concentration of glucose in blood is controlled within narrow limits by many hormones, the most important of which are produced by the pancreas.
The most frequent cause of hyperglycemia is diabetes mellitus resulting from a deficiency in insulin secretion or action. A number of secondary factors also contribute to elevated blood glucose levels. These include pancreatitis, thyroid dysfunction, renal failure, and liver disease.
Hypoglycemia is less frequently observed. A variety of conditions may cause low blood glucose levels such as insulinoma, hypopituitarism, or insulin induced hypoglycemia. Glucose measurement in urine is used as a diabetes screening procedure and to aid in the evaluation of glucosuria, to detect renal tubular defects, and in the management of diabetes mellitus. Glucose measurement in cerebrospinal fluid is used for evaluation of meningitis, neoplastic involvement of meninges, and other neurological disorders.
The measurement and interpretation of glucose concentrations is an area of much confusion. Plasma glucose is about 12% greater than that of whole blood because plasma has a higher water content as it contains no red blood cells. In the fasting state there is little difference between arterial, capillary and venous glucose concentrations but after carbohydrate intake glucose concentration in arterial and capillary samples can exceed those of venous samples by as much as 1.8 mmol/l. This is of particular practical importance in the interpretation of oral glucose tolerance tests.
For the measurement of glucose a specimen containing sodium fluoride to inhibit glycolysis and stabilise the glucose concentration is preferred. If blood is collected into a tube without preservative, glucose concentration can decrease by as much as 7% each hour as a result of glycolysis. Clinically significant decreases in glucose concentration have been reported even with use of preservative. If a tube without preservative is used and delay in transit to the laboratory is anticipated, storage at 4oC is preferable.
