The CGMS helps you stay aware of your current glucose levels. Use it along with traditional monitoring. The system discovers patterns in glucose levels. You and your health care team can use this detail to decide on the best treatment. While anyone with diabetes can use a CGMS, it is especially useful for those who:
It is not necessary to use the CGMS all of the time. You may use it only now and then to fine tune diabetes control. It can also show whether changes to diabetes management have made a difference.
A CGMS consists of three parts. It has a disposable glucose sensor, a transmitter, and a monitor (receiver).
The small sensor is a sterile, disposable device inserted under the skin. Insertion is quick, and is usually not painful. Every 10 seconds, the sensor measures glucose in the interstitial fluid (which surrounds the cells of the body). Wearing the sensor will not affect your daily activities. The sensor must be regularly removed and replaced. Time between changes will vary depending on the system. It is usually done every three to seven days.
The transmitter snaps into the sensor. It sends information about glucose levels to the monitor wirelessly. The transmitter is slightly larger than a quarter and thin as a stack of four quarters (0.89 centimetres). It is designed to stay in place close to the skin when connected to the glucose sensor. However, tape or transparent dressing can also hold both the sensor and transmitter in place. Since the transmitter is waterproof you can shower or bathe with it in place. You can also engage in water activities while wearing the transmitter and glucose sensor.
The monitor attaches to a belt or your clothing. It automatically and continuously displays an updated average glucose value every five minutes. Some devices can do this for up to 168 hours.
The monitor also shows whether the glucose values are rising or falling, using trend graphs and arrows. Trend graphs display patterns over the last three, six, 12 and 24 hours, giving a clearer picture of glucose levels over time. Trend arrows show the direction of glucose levels and rate of change, anticipating what will happen next.
All of the collected information can improve your understanding of how diet, exercise, medication and stress affect glucose levels. It becomes easier to adjust treatment.
CGMS have several different alerts that warn about oncoming lows and highs. Alerts can be set to vibrate, ring, or do both. There are three different types of early warnings.
Note that the level of glucose in interstitial fluid can lag behind the level in blood. For this reason, any high or low reading on the CGMS must be confirmed with a fingertip measurement of blood glucose.
In Canada, the only system currently available is the Guardian® REAL-Time Continuous Glucose Monitoring System by Medtronic. Two other systems are available in the United States - the SEVEN® PLUS (DexCom™) and the FreeStyle Navigator® (Abbott).
Each day, the CGMS must be calibrated. To do this, enter two to four blood glucose values obtained by a finger stick blood glucose test. You still need to take finger stick readings at different times of the day using a blood glucose meter. Enter these readings into the monitor within five minutes of taking the test.
For best results, do finger stick checks when blood glucose is at ‘steady state.’ In steady state, blood glucose levels are not changing rapidly. Avoid calibrating the monitor after eating, after an insulin dose, or within three hours of exercise.
The Guardian® system can store up to 31 days of blood glucose information. You can download results to a computer. Information will appear as graphs or charts to show patterns of blood glucose changes. Record insulin doses, exercise, and meals and snacks in a log book or your computer using the software program supplied.
You and your health care team can consider all of the information collected when reviewing your blood glucose levels. Decisions about your treatment plan can then be aimed at correcting any problems. To see if the changes have worked, continue to test with the CGMS and follow up with an A1C test.
This system’s main advantage is that it can identify changes and trends that would not otherwise be noticed with standard A1C and a limited number of finger stick tests.
A CGMS is particularly useful for:
CGMS does have drawbacks. First, it must be calibrated using traditional blood glucose testing methods. Low and high blood glucose levels must be confirmed with finger stick measurements before taking action.
Radios or television sometimes interfere with the wireless system. Moving away from the radio or television may help. Other wireless devices, such as cell phones, cordless phones and computer networks, may also interrupt communication. This will not cause incorrect data nor harm the system.
Alarms that provide protection from oncoming highs and lows can be disruptive if high and low limit alerts are set too close together. Adjust the settings to prevent constant alarm alerts.
Most importantly, it takes time for interstitial glucose levels measured by the sensor to catch up with glucose values in blood. ‘Real time’ for the CGMS may be a five to 20 minute wait. This varies between individuals.
Lag time is not important when blood glucose levels are constant. However, if blood glucose levels change rapidly, a normal reading on the CGMS may in reality be an out-of-range blood glucose requiring treatment.
A version of the Guardian® REAL-Time System is the iPro™ Continuous Glucose Monitor. Your health care provider assists you. While this system has a glucose sensor and transmitter, it does not have the monitor or viewing screen. The health care provider will insert the sensor. You do little apart from checking blood glucose four times per day and recording this information along with a list of your food and activities.
After three days, return the transmitter to your health care provider. The stored blood glucose information is retrieved on a computer and printed out. You and your team can review this information and use it in managing your diabetes. This service is available at some Safeway pharmacies.
This service is available at three Safeway Locations: Lawson Heights Safeway Pharmacy, Audrey McLelland, 134 Primrose Drive, Saskatoon, Saskatchewan (306) 249-1468; Landmark Safeway Pharmacy, Elaine Cooke, 300-20201 Lougheed Hwy., Maple Ridge, British Columbia (604) 460-7200; and Clearbrook Town Square Safeway Pharmacy, Sharon Giles, 100-32500 S. Fraser Way, Abbotsford, British Columbia (604) 852-3558.
If you are using a CGMS, consider the absolute value of the blood glucose level on your monitor as well as the trend. For instance, if you have blood glucose of 5.5 mmol/L on the CGMS you may leave it alone if it has been consistent for several readings. The reaction is different if you have the same blood glucose level but know it has dropped quickly over a short period of time. In this case, you should do a finger stick test to check for low blood glucose.
Continuous monitoring systems are not covered by provincial drug plans. However, private insurance may cover them. Check with your carrier. Since the technology is new, it may not be considered an established standard of treatment. The cost is high, as the sensors need to be replaced often. The monitor will be under warranty for one year, and the transmitter for six months. Individual insurance companies may agree to pay, on a case-by-case basis, after talking with your doctor. The CGMS companies provide guidance to help with the insurance companies.
You might also pay for the CGMS yourself and then claim it on your annual income tax. (Talk to your financial advisor.) The Guardian® REAL-Time System currently costs about $2,000. This includes the transmitter, monitor, software to download data onto your computer, and four sensors. You can buy the system directly from the company. Extra sensors will be around $200 for a box of four. You can find them in your Safeway pharmacy.
A CGMS system allows us to see, for the first time, what happens to glucose levels minute by minute throughout the day. Trends can be evaluated in greater detail. For some, a CGMS dramatically affects the way their diabetes is treated.
Using a CGMS, blood glucose levels can be seen as the body reacts to insulin, exercise, food, stress and other factors. This data can be useful in adjusting insulin for food intake and correcting high blood glucose. Monitoring during times when blood glucose levels are not normally checked, such as during sleep, can identify problems with insulin doses. Monitors can also warn of high and low blood glucose. This way, you can correct after confirming with a finger stick test, even if there are no symptoms. While there are limitations to CGMS, studies have shown that those using it have fewer high blood glucose levels and reduced A1C levels.
Spending less time with low or high blood glucose reduces the risk for a number of serious short and long-term complications related to diabetes. By measuring glucose levels continuously, a CGMS provides more and better information than traditional finger stick measurements alone. It is likely to improve diabetes management.