By Jan Chait | October 17, 2006 11:00 am
Several years ago, my daughter decided she needed to live in Kansas. That would have been fine except that, for some reason, she insisted on taking my grandchildren with her. That, in turn, necessitated my going to Kansas on occasion.
On one trip, as I was taking the children back home after they’d spent some time with me, I happened to be wearing a continuous glucose monitor—the kind you wore for three days, then the doctor downloaded the data. Imagine my horror when I later saw the data and realized that, while I was driving my two small grandchildren home, my blood glucose had been in the 40s for more than an hour at one point.
Today, that wouldn’t happen: I’ve treated myself to a new continuous glucose monitor (CGM) that displays results every five minutes and sounds alarms if my glucose levels go above or below certain parameters that I have set myself.
Less than three hours out of the box, my new “toy” proved its worth by showing me that my blood glucose was on a downward trend and alerting me to the fact that I was about to enter the wonderful world of hypoglycemia before I actually got there.
There are three CGMs currently on the market that allow you to monitor glucose values in pretty close to real time: the Guardian RT and REAL-Time Continuous Glucose Monitoring systems by Medtronic MiniMed and the STS system from DexCom. Expected soon is the FreeStyle Navigator from Abbott Diabetes Care, which is currently under review by the U.S. Food and Drug Administration.
With each of these systems, you insert a minimally invasive sensor into your body. The sensor measures the glucose in your interstitial fluid (a fluid that surrounds your body’s cells, providing nutrients and helping to eliminate waste) and relays that information to a transmitter. Depending on the CGM, the transmitter is either snapped into a mount on top of the sensor or adhered separately to your body. In most cases, the transmitter sends a wireless signal to a receiver, a device about the size of a pager that displays readings and stores information. Medtronic’s REAL-Time system transmits glucose values to its Paradigm insulin pump.
But so much for the mechanics: This thing is awesome! Just as I discovered my body’s rhythms eight years ago after switching from multiple daily injections to an insulin pump, I’m now learning about how my glucose levels react to different things in what amounts to a movie instead of the snapshots given by finger sticks.
For example, I use pramlintide (brand name Symlin) along with my insulin pump. At meals, I had been giving myself two-thirds of the insulin I needed to cover my food immediately and spreading the remainder out over two hours. After using the CGM and seeing my glucose levels plunge shortly after giving myself Symlin and insulin, though, I experimented until I found the correct ratio—which, for me, turned out to be the exact opposite of what I had been doing. Now, instead of two-thirds up front and one-third over two hours, I give myself one-third of my insulin up front and the remainder over two hours.
I’ve found out that insulin begins working in me a lot faster than I ever thought it did.
I can look at the trends on the screen and tell when my glucose is on the way up—or down—and make the appropriate corrections in a more timely fashion.
For now, I’m getting the micromanagement down, but I need to work on “macromanagement.” For example, I found out that my glucose goes steadily down all night long. Oops! I need to lower my overnight insulin dosage. I just need to figure out when and by how much.
A CGM has other advantages, too. Want an idea of where your glucose level is at when you’re in the car? Grab the receiver off the seat or out of the console and press a button (which would have been handy on that drive to Kansas). Want to find out where your numbers are in the middle of the night without totally waking up to head for your meter and check? Reach over to the nightstand and press a button.
If your glucose level goes below a level that you have specified in the middle of the night (or any other time), you get an alarm. Same with a high level.
CGMs are in their infancy now and have their glitches. The current and forthcoming models are designed to be used along with a blood glucose meter, not instead of one. Because changes in interstitial glucose levels can lag several minutes behind blood glucose levels, you must confirm any value with a blood glucose meter before taking treatment action. But I do believe that CGMs are the coming thing and, eventually, will replace meters, just as meters replaced urine testing. And, hopefully, insurance will begin covering them soon.
In the meantime, I’ve been using a CGM for less than one month now and already don’t know how I got along without it.
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