The daily blood glucose (also known as blood sugar) concentration should remain constant, as food is ingested, broken down to simple monomers, and used to produce energy, water, and carbon dioxide. The metabolism of glucose is a tightly regulated series of biochemical reactions; but its most important regulator is the hormone insulin, which is responsible for initiating a series of signal transduction events that lead to the breakdown or storage of glucose molecules (Mathews & Van Holde, 1996). When insulin is missing or when the body could not respond to insulin, blood glucose levels may either increase or decrease disproportionately.
This leads to the major disease diabetes, which can wreak havoc with the metabolic organs of the body, leading to secondary complications like blindness and liver failure. However, diabetes can be managed with the proper diet and exercise regime. Thus, it is important to monitor blood glucose levels to identify the steps or the degree of management necessary to maintain blood sugar at the correct metabolic levels. The blood glucose test measures glucose in the blood at the time when sample is collected. It can detect both hyperglycemia and hypoglycemia, diabetes, and is used to monitor the blood sugar in diabetics.
There are several times when blood glucose may be measured: after an 8-10 hour fast, any random time, exactly two hours after a meal (post prandial), and during an oral glucose tolerance test (OGTT) (American Asociation for Clinical Chemistry, 2009) (Rea, 2007). Fasting and OGTT are recommended to diagnose diabetes, but tests are to be done twice at different periods to confirm a diabetes diagnosis. Random blood glucose tests are given during the day to see the variation in blood sugar (normally, blood sugar does not vary through the day).
Testing for blood glucose can be used in screening apparently healthy individuals for diabetes. This is because diabetes can develop anytime and being asymptomatic, it can be at an advanced stage before detected. Blood glucose screening can be done during school fairs, company events, and during a routine physical examination. Some people are at higher risk of diabetes especially those who are overweight, aged more than 40 years old and with a family history of diabetes (American Asociation for Clinical Chemistry, 2009).
Other symptoms of diabetes are fainting or unconsciousness. There are several methods of testing blood sugar even at home (reviewed by Seibel 2009). The traditional method involves pricking the finger with a sharp needle, placing a drop of blood on a strip and having a meter read the sugar concentration. There are many types of meters used, with speed and other advanced features incorporated into newer models. The meters can be programmed to store, retrieve and graph data collected over time.
There are some meters that test the blood glucose in other sites of the body like the thigh, forearm and thumb, although results can be different from those taken from the fingertips. The fingertips are more indicative of rapid changes in blood sugar, like what happens after a meal. The pain brought about by pricking fingers with needles led to the development of lasers to take blood samples, thereby reducing the pain. Another method is the continuous glucose monitoring system, which involves a very small plastic catheter inserted under the skin, collecting small amounts of blood and measuring the sugar content over a few days.
A similar device, the Freestyle Navigator Continuous glucose Monitoring System was used in the daily management of Type I diabetes in children. It was found that its use in children was also feasible and useful in real-time continuous glucose monitoring and management (Diabetes Research in Children Network (DirecNet) Study Group, 2002). In 2001, the US-FDA approved the use of the Gluco-Watch, which is worn similar to a watch, to help diabetics measure their blood sugar throughout the day. Tiny electric currents measure blood sugar levels, and values could vary widely due to this.
In the clinical setting, blood glucose is measured using the enzyme glucose oxidase, which converts glucose in the presence of oxygen to gluconic acid and hydrogen peroxide. The reaction is carried out in the presence of the enzyme peroxidise which catalyzes the conversion of the hydrogen peroxide to water and oxygen. 4-aminophenazone, a colourless compound takes up the oxygen, and in the presence of phenol, forms a magenta chromogen. The concentration of this chromogen is determined by its absorbance at wavelength of 515 nm.