Figure 2.1: Glucose meter

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1 CHAPTER TWO: MONITORING TECHNOLOGIES 2.1 Introduction Glucose monitoring is a method of self-testing glucose (blood sugar) levels for the management of diabetes. Traditionally, it involves pricking the finger or an alternate site such as the arm or thigh for a sample of blood and placing that sample on a test strip. A glucose meter then analyzes the strip (see figure 2.1). The meter digitally displays the glucose level as a number in milligrams per deciliter (mg/dl). Some meters give the possibility to store data, and download them computers for further analysis. Figure 2.1: Glucose meter Other methods of glucose monitoring exist, including visually read blood and urine strips and home glycohemoglobin tests. However, the glucose meter is considered the most accurate tool for measuring day-to-day glucose control at home. Three trends are emerging in self-monitoring of diabetes during the early 21st century. At this time we are seeing the increasing availability and use of: 1) continuous glucose monitoring; 2) home testing of biomarkers of glycemic control; and 3) the early stages of development of closed loop control systems. The current technology for self monitoring of blood glucose levels has been well established since the 1980's. This practice is beneficial to patients with diabetes from both a clinical and an economic standpoint. Knowledge of the blood glucose levels that are measured can allow a patient to select an appropriate dose of insulin to regulate the blood glucose levels. Continuous glucose monitoring is the next step in glucose monitoring. This practice is not yet widely established, but evidence supporting its use is accumulating. The information provided by this continuous glucose monitoring can permit significantly more adjustments in insulin dosing and other therapies than spot testing from self monitoring of blood glucose can provide. Continuous glucose monitoring technologies for automatic collection of data have spurred interest in alternate site testing of blood glucose and noninvasive glucose monitoring, as additional tools for obtaining information about glucose levels. After glucose level measurements, the next step in determining insulin dosing is not yet commercially available but will revolutionize diabetes management. The future 14

2 technology that will permit adjustment of insulin dosage and with automatic control is closed loop control. This approach, also known as the artificial pancreas, is currently being developed. An artificial pancreas will link continuous blood glucose measurement with automatically controlled insulin delivery, using non-living components made of silicon, plastic, and metal. Recent research suggests that half or more of diabetes patients have poor glycemic control and that many admit not checking their glucose often enough. Regular glucose monitoring is essential in avoiding serious consequences such as diabetic retinopathy and diabetic coma. 2.2 Benefits and risks of glucose monitoring All people with diabetes benefit from glucose monitoring. For example, people with type 1, type 2, gestational diabetes or other forms of diabetes who take insulin or antidiabetic agents can judge how well these drugs are working. Monitoring provides information on how much medication is needed to counter the rise of glucose (blood sugar) after a meal. These medications may put a person at risk for low glucose (hypoglycemia). Monitoring will reveal if levels are too low. Patients who manage diabetes with a diet and exercise plan can benefit from feedback on how well their exercise and food choices are working. During pregnancy, glucose monitoring guides the treatment adjustments necessary to keep the woman and her fetus healthy. Glucose monitoring is an effective way to control levels of blood glucose and offers many possible benefits to diabetes patients. Potential benefits of glucose monitoring include: Detecting and preventing hyperglycemia (high glucose), hypoglycemia and insulin shock. Preventing or delaying long-term complications of diabetes, including diseases of the eyes, kidneys, nerves and blood vessels. Uncovering the effects of food, exercise, stress, illness, insulin and other medications and other factors on glucose levels. Keeping track of glucose levels over time and determining trends and patterns. Assisting in making day-to-day decisions for glucose management, including meal size and dosage of insulin and other medication. Confirming that suspicions of low or high glucose are accurate and not the result of something unrelated to diabetes. Alerting to emergency situations so immediate action can be taken to lower or raise levels of glucose. Determining the need for starting insulin therapy. Identifying where changes in the diabetes management plan are needed. Deciding what action is needed when a person is suffering from an illness. The potential risks associated with glucose monitoring involve use of a glucose meter. A number of factors can make meter readings inaccurate, including machine malfunctions or human error 15

3 2.3 Methods of glucose monitoring The glucose meter is the most popular method of glucose monitoring. Although other methods exist, the glucose meter is considered the most accurate home method for measuring day-to-day control of glucose (blood sugar). A glucose meter, also called a glucose monitor, is a small, is a small, portable device that lets patients check their levels of blood glucose. Testing glucose with a typical meter requires a person to use a lancet and place a small sample of blood on a test strip. Test strips are coated in chemicals that combine with glucose. The meter then analyzes the strip. Alternatives to the glucose meter include: - Visually read blood glucose strips These strips require a blood sample to be applied to a chemically coated test strip. The test pad on the strip then changes color accordingly. The more glucose is present in the blood the greater the color change on the test pad. The user then compares the color on the test pad to a color chart on the side of the vial and estimates their level of blood glucose. - Visually read urine strips Glucose can also be present in urine, and there are several urine tests available on the market. Some require the strip to be dipped into a cup of urine, and others need to be passed through a stream of urine. The chemically coated test pad then reacts with the glucose in the sample and changes color accordingly. The test pad is then compared to a color chart on the side of the vial. Like visually read blood strips, visually read urine strips are beneficial when patients forget their meter or when their meter is malfunctioning. They are also easier to use when traveling. Although urine testing is less intrusive than blood testing, it is less accurate. Urine strips should be used for glucose measuring only when blood testing is not an option. Among the drawbacks of visually read urine strips: Hypoglycemia is not detected, results are not current; urine strips do not report what glucose levels are at the moment, but rather what they were several hours ago. Current readings are necessary for deciding insulin dosage, handling emergencies and evaluating treatment programs. Results do not provide details. Urine strips do not report when levels were high or how high they were. Results are not exact. Urine glucose levels are more of an average value than blood glucose levels. Many factors can alter results. Aspirin, fluid intake, vitamin C, dehydration, and failure to fully empty the bladder on the previous trip to the bathroom may alter urine strip results. - Glycohemoglobin test (A1C test) This test measures a person s average blood glucose level over a two- to three-month period. Hemoglobin is a protein component of red blood cells that transports oxygen to the cells in the body. Hemoglobin combines with blood glucose to make glycosylated hemoglobin. The test shows the amount of glucose that sticks (glycates) to the red blood cells, which is proportional to the amount of glucose in the blood. A hemoglobin A1c goal for people with diabetes is less than 7 percent but not everyone can meet that goal. 16

4 Each person should try to get as close as possible. A change in treatment plan is almost always needed if your test result is over 8 percent. Having a glycohemoglobin test several times a year is a good way to determine if glucose levels are under control. Patients who are not meeting their treatment goals should have the A1C test four times a year, or as recommended by their physician. Traditionally assessed in a physician s office, glycohemoglobin can now be measured with home testing kits. Most require patients to take their own blood sample and mail it to a lab for results. At least one version allows patients to see an immediate digital reading, but it is a one-time-use test. However, home monitoring cannot replace the regular A1C test performed by a physician. 2.4 Frequency of monitoring People with diabetes need to consult their physician about often to test glucose (blood sugar) levels. Some patients must test more often than others. Testing three to four times a day, sometimes more, is usually recommended for people who take insulin, because their glucose levels tend to fluctuate more throughout the day. Patients may need to test more often if they are sick or have a change in their normal routine such as an increase in stress or exercise. Patients aiming for normal or near-normal glucose levels may be advised by their physician to monitor four or more times a day. Studies have shown that when monitoring drops to less than four times a day, glucose control worsens. People taking anti-diabetic agents will be advised to monitor frequently when their physician is trying to find the right dose or when there is a change in their diabetes care plan, such as an increase in insulin. Once a physician has decided if any changes are needed, recommended monitoring may be reduced to once or twice a day. When diabetes is managed without medications and glucose levels are under control, monitoring might be less frequent. Useful times for glucose monitoring include: Before meals or a big snack (preprandial); insulin doses can be adjusted based on results. One to two hours after meals or a big snack (postprandial); results can show the effects of various foods on glucose levels. When a dose of rapid-acting insulin is taken before meal, results can show its effectiveness. Before bedtime; when the reading is low, steps can be taken immediately to raise the level of blood glucose. Insulin doses can be adjusted if results continue to be low. Early morning (2 or 3 a.m.); early-morning blood glucose tests can provide information on overnight glucose. Insulin doses can be adjusted to prevent nighttime hypoglycemia. Immediate action can be taken to raise glucose levels. 2.5 Advanced technologies in Glucose monitoring Scientists are trying to make glucose monitoring more convenient, comfortable and accurate. Available advances include: -Continuous Glucose Monitoring System (CGM) In order to obtain better knowledge of blood sugar levels throughout the day and over a large period of time instead of just at obscure times, continuous glucose monitors were developed. This constant feedback helps patients and their physicians identify when they are hypoglycemic or hyperglycemic so that they can make optimal decisions about 17

5 treatment plans and prevent these conditions. Monitoring glucose levels throughout the day also reveals surprising peaks or dips in levels that would otherwise be missed by just measuring a few times a day. [5] These monitoring systems consist of a small glucose sensor which is inserted subcutaneously to measure the change in glucose in the interstitial fluid. This is considered minimally invasive since no blood vessels are pierced even though the skin barrier is crossed. This change in blood sugar is sent to and stored in a monitor which can carry up to 3-4 days of data. The monitor must be calibrated each day by measuring blood glucose at least three varying times using a standard blood glucose monitor. Patients should also entire other important information such as a patients insulin doses, food information, and exercise pattern into the monitor. [6] Once calibrated and given appropriate information the monitor can measure a patient s blood sugar every 1-10 minutes for up to 72 hours [5]. At this point, the monitor is returned to the physician where it is connected to a docking station and computer to allow analysis of the patient s glucose levels and treatment plan. Many glucose monitors also allow patients to enter a range so that if their glucose level falls above or below this range an alarm sounds to alert the patient of this problem. Some monitors also provide patients with their current glucose level. Since glucose monitors sometimes measure a time-lagged blood sugar level if the provided value is irregular, patients should not immediately adjust insulin doses but rather test their blood sugar by performing a finger prick and evaluating with a standard blood glucose monitor. Based on the finger prick value patients may adjust insulin appropriately. [5, 6] Several of these systems have been approved, and researchers are developing others. A typical CGM device measures glucose every five minutes for up to three days and is intended for occasional use, not to replace fingerstick testing. A device approved by the FDA in 2007 allows monitoring for up to seven days. One CGM device is worn like a wristwatch; others are pager-size devices with a needle-like sensor that is inserted into abdominal skin (figure 2.2). The information is stored in the monitor s memory and then transferred to the physician s computer. Figure 2.2: Glucose Continuous monitoring system components 18