Continuous Glucose Monitoring: Practical Uses in Diabetes

Anne L. Peters, MD, CDE


January 25, 2013

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Hi. I am Dr. Anne Peters from the Keck School of Medicine of the University of Southern California in Los Angeles. Today I am going to talk about practical applications of continuous glucose monitoring. I bring this up because recently Dexcom's new G4, their fourth-generation device, has been approved and is available for use. This is a big step forward in continuous glucose monitoring. By next spring, another new continuous glucose monitor by MiniMed may be approved. This technology is advancing, and it is important to understand how it can be applied. First I will show you the devices, and then I will discuss the pros and cons of using them.

With Dexcom G4 continuous glucose monitoring, the system is pretty much the same [as it has been]. The patient can easily insert the sensor under the skin -- for example, on the abdomen or the back of the arm. A small transmitter is then placed on top of the sensor. The transmitter sends the interstitial glucose value to the device itself so the patient can see the blood sugar level. It transmits this information wirelessly every 5 minutes, so a patient can get a sense of whether their blood sugars are going up, going down, or staying the same.

The new Dexcom G4 is somewhat smaller [than the earlier-generation device]. It is not as wide, similar to an iPhone, and is easy to put in your pocket. It has a pretty good range so that you can be moving around in your house and the signal will still reach the device. The patient can turn it on and see exactly what is happening to the blood sugar -- [not only the level, but the trend up or down]. A blood sugar level that is 100 mg/dL and is going up may require much different treatment from a blood sugar level of 100 mg/dL that is flat and the patient might be just fine. Or, if a blood sugar level is falling fast, it may mean that the patient needs to ingest carbohydrate to avoid a low. The patient can get a lot of information in real time from this device. Then, in my office, I download the device and interpret the data for the patient so I can help the patient analyze the data retrospectively, so that in real time patients can make more reasonable choices.

In addition to the fourth-generation Dexcom, which is more accurate than earlier models, we also have the new MiniMed continuous glucose monitor, the Enlite™ sensor, which is supposed to be available in the spring. This is similarly inserted under the skin and taped down. In most cases, this device is talking to the patient's insulin pump. The insulin pump has the tubing necessary to give the patient insulin, but now this pump also becomes the receiver for the signals from the sensor. The patient can look at the pump and see what the blood sugar levels are doing. This device also has alarms [to warn the patient when levels are too high or too low].

A lot of patients want the pump to automatically give insulin based on their blood sugar levels, but that is not what happens. This is truly a sensor, and the patient then needs to use the Bolus Wizard [calculator] to interact with the pump to calculate the insulin dose. That coupling of the sensor and pump is part of the development of the artificial pancreas. Substantial research is being done to make pumps that can use continuous glucose monitoring data so that the patient does not have to think as much about diabetes management. [Those advances] are in the future. For now we have sensors that sense interstitial fluid, giving continuous real-time data, and we have pumps that patients interact with to give themselves insulin. You can couple the MiniMed sensor with the MiniMed pump. The Dexcom device does not interact with a pump, although the manufacturer is working on collaborations with some pump manufacturers.

I personally try wearing these sensors because I find it interesting. I do not have diabetes, but I am geeky enough to enjoy watching my blood sugar levels go up and down a bit. I also want to understand what kind of burden it is for our patients to wear these devices. One of the burdens is having too many alarms. A lot of patients do not want to be reminded constantly that they have diabetes, and they are leery of the alarms going off when the blood glucose levels, or the interstitial glucose levels on the sensors, are not accurate. This next generation of continuous glucose monitors is more accurate than the previous generation. I think each subsequent generation will improve in accuracy. I often take out the high alarms so patients are not "alarmed" if their blood glucose levels are too high. I keep the safety alarms on for too low, or for patients who seem to be approaching a low. Then, as the patient stabilizes, I may put the high alarm back on. I want to reduce some of the burden on patients. People do not want to be "alarmed" all of the time, particularly if accuracy is an issue.

I hope this brings you up to date on continuous glucose monitors. I know that progress is slow, but I also believe that this kind of device is helping us better manage our patients with diabetes, particularly those who take insulin.

This has been Dr. Anne Peters for Medscape. Thank you.