Another, Expensive, Diabetes Myth   (July 30, 2011)

I think it's time to add another diabetes myth for consideration by those of you using Continuous Glucose Monitoring, or who might be thinking about starting. I have been using a continuous glucose monitor for almost a year now.

The myth: You should change your CGM sensor when the manufacturer says to do so.

For those of you interested in the technical details about CGM: The device I'm using, the Dexcom Seven Plus, has several components: two are permanent (a receiver that displays the results and a transmitter that sends glucose information wirelessly from the sensor to the receiver), and the third is a replaceable gadget that attaches to the skin, and which combines several things: a thin wire called a "sensor" that goes through the skin and which senses subcutaneous glucose levels, a plastic unit attached to the sensor that remains on the surface of the skin and holds the transmitter as well as the exterior connections for the sensor, and an adhesive patch that holds the entire gadget on the skin. The adhesive patch, by the way, is frequently inadequate, and the manufacturer advises using additional medical tape to help hold the gadget to the skin. Using medical tape definitely helps prolong the stickiness of the provided adhesive patch, thereby helping keep the thing from detaching from the skin.

This replaceable sensor gadget is supposed to be used for seven days (for my brand of CGM), and then it's supposed to be changed. (For other brands of CGM, the sensors are recommended to be used for shorter periods of time.) Changing the gadget is relatively simple: removing the previous sensor by yanking off the sensor and adhesive patch, detaching the transmitter, inserting a new sensor gadget, attaching the transmitter, adding extra tape, and recalibrating the system after two hours.

But after seven days the sensor is still working fine. So why change, just because the manufacturer says to? After all, each sensor costs a huge chunk of change: a box of four carries a list price of $616.81. That's over $150 per sensor, and I've become unwilling to burn the extra bucks, whether mine or the insurance company's, simply because seven days happens to be the longest duration that the sensors were tested in clinical trials. It's just as easy to verify that the device is working during the second week as it had been during the first week, as checking a blood glucose level to keep the device calibrated is necessary several times a day. The biggest problem I've noticed during a second week is that sometimes the device starts showing increased number of error messages after prolonged use.

There are many mentions on the Internet of using different brands of CGM sensors for longer than the recommended time, and I'm now routinely using my DexCom sensors for two weeks, and cutting the cost in half. Should I try for even longer? Probably not. The adhesive is definitely getting raunchy by then, and as I mentioned, sometimes the device starts displaying increased numbers of error messages. And in theory, the longer there's a gadget penetrating the skin layer, the higher the risk of infection if bugs sneak in.

But back to my point: using CGM sensors for longer than the recommended duration is possible, and should be considered by anyone using CGM.