determination of blood glucose

Blood glucose
Glucose is the most important carbohydrate fuel in the body. In the fed state, the majority of circulating glucose comes from the diet; in the fasting state, gluconeogenesis and glycogenolysis maintain glucose concentrations. Very little glucose is found in the diet as glucose; most is found in more complex carbohydrates that are broken down to monosaccharides though the digestive process. Glucose is classified as a monosaccharide because it cannot be broken down further by hydrolysis. It is further classified as a hexose because of its six-carbon skeleton and as an aldose, because of the presence of an aldehyde group on carbon1.high blood glucose levels is referred to as hyperglycemia; low levels are referred to as hypoglycemia. Diabetes mellitus is characterized by persistent hyperglycemia.
The international standard way of measuring blood glucose levels are in terms of a molar concentration, measured in mmol/L (millimoles per litre; or millimolar, abbreviated mM). In the United States, West-Germany and other countries mass concentration is measured in mg/dL (milligrams per decilitre).
Since the molecular weight of glucose C6H12O6 is 180, for the measurement of glucose, the difference between the two scales is a factor of 18, so that 1 mmol/L of glucose is equivalent to 18 mg/dL. Ordinarily the concentration of glucose in the blood is maintained at a relatively stable concentration from 80 to 120 mg/dl (4.4-6.6 mmol/L).
The body s homeostatic mechanism keeps blood glucose levels within a narrow range. It is composed of several interacting systems, of which hormone regulation is the most important.
There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels:
• Catabolic hormones (such as glucagon, cortisol and catecholamines) which increase blood glucose;
• Anabolic hormone (insulin), which decreases blood glucose.

Conditions associated with hyperglycaemia
1-Diabetes mellitus
2-Cushing s syndrome (Adrenal cortical hyperactivity)

3-Hyperthyroidism

4-Acromegaly (increase growth hormone)

5-Obesity

6-Pheochromocytoma (increase catecholamines)

Measuring blood glucose level
Glucose concentration may be determined in whole blood, plasma, or serum samples.
Rapid separation of the sample or cooling will prevent glycolysis and will allow the sample to be used for other determinations. Unhemolyzed samples that have been separated within 30 minutes of drawing are generally considered adequate. Rapid cooling of the sample followed by centrifugation is even more effective in preventing glycolysis. If the specimen has been promptly centrifuged, it is reasonable to ask the laboratory to measure the glucose concentration even though a sodium fluoride (green top) tube was not used.
Glucose oxidase is widely used method for measuring blood glucose level. In the glucose oxidase assay, the glucose is first oxidized by glucose oxidase to produce gluconate and hydrogen peroxide. The hydrogen peroxide is then be used to oxidize a chromogen to produce a red colored compound which can measured by spectrophotometer. For example, hydrogen peroxide together with 4 amino-antipyrene (4-AAP) and phenol in the presence of peroxidase yield a red quinoeimine dye that can be measured at 505 nm. The absorbance at 505 nm is proportional to concentration of glucose in the sample.




Diagnostic criteria (adults) of diabetes mellitus
1. Classic symptoms and random glucose >200 mg/dl
(more than once)
2. Classic symptoms and Fasting glucose ?126 mg/dl
(more than once)
3. OGTT† ?200 mg/dl (11.1 mmole/L)