Diabetes: Continuous Glucose Monitoring

A continuous glucose monitoring system (CGMS) is an FDA-approved device that records glucose levels throughout the day and night. There are a number of technologies that are being tested but the only approved device -- Medtronic's MiniMed device-can provide up to 288 glucose measurements every 24 hours. The system is used to measure an average blood glucose for up to 3 days, while the person with diabetes continues daily activities at home.

How Does the Device Work?

First, a tiny glucose-sensing device called a "sensor" is inserted just under the skin of your abdomen. The insertion is quick, and is usually not painful. It's very similar to insertion of an insulin pump catheter. Tape is used to hold it in place.

The sensor measures the level of glucose in the tissue every 10 seconds and sends the information via a wire to a pager-sized device called a "monitor" that you attach to a belt or the waistline of your pants. The system automatically records an average glucose value every 5 minutes for up to 72 hours.

Results of at least four finger stick blood glucose readings taken with a standard glucose meter and taken at different times each day are entered into the monitor for calibration. Any insulin taken, exercise engaged in, and meals or snacks consumed are both entered into a paper-based "diary" and recorded into the monitor (by pushing a button to mark the time of the meals, medication, exercise, and other special event you wish to record).

After 3 days, the sensor is removed at the doctor's office and the information stored in the CGMS is downloaded into a computer. You and your doctor or diabetes health care team can then review your glucose levels in relation to the other data collected and make any necessary adjustments in your diabetes management plan. The information will be presented as graphs or charts that can help reveal patterns of glucose fluctuations.

When Is the Device Used?

The CGMS is not intended for day-to-day monitoring or long-term self-care and it is not a replacement for standard blood glucose monitoring. It is only intended for use to discover trends in glucose levels. This helps your health care team make the most appropriate decisions regarding your treatment plan.

The main advantage of continuous glucose monitoring is that it can help identify fluctuations and trends that would otherwise go unnoticed with standard HbA1c tests and intermittent finger stick measurements.

For example, the device can capture dangerously low overnight blood glucose levels which often go undetected, reveal high blood sugar levels between meals, show early morning spikes in blood sugar, evaluate how diet and exercise affect blood sugars, or provide up to a 72-hour complete review of the effects of changes made to your therapy by your health care team.

Your doctor can prescribe the procedure as often as he or she believes it necessary to properly evaluate your blood glucose patterns. Continuous monitoring is reimbursed by Medicare and covered by many private insurance plans (check with your individual carrier).