Some basics about the Dexcom

I got two similar questions recently about the Dexcom 7 continuous glucose monitor (CGM) and I realized it's probably worth summarizing what I know about it for those who might be interested in using one. So here's a fairly long post with most of what I know about this interesting device. Note that the Dexcom 7 is officially approved for use in adults, but there are some folks on that list who are using it successfully with their children.

For the record. I start using the Dexcom 3 in March 2007, after a one week free trial. I switched to the Dexcom 7 on July 24th 2007 and have been using it ever since. After 35 days I'm on my 3rd 7-day sensor, so I'm getting an average of at least 12 days out of each one. Remember the sensors are approved for 7 days of use, but most people continue to use them after the seven days are up. I'll post in the future about how to do this, because it's not immediately obvious for everyone.

There are several bloggers who have posted a lot about their Dexcom experiences. You can find a list using the Diabetes Search Engine. Anthony has his Dexcom Seven blog, and Clemma has her Comrade Dex blog, both of which are very informative.

Trying out the Dexcom

You should not purchase a Dexcom without first trying it out. The cost of a Dexcom 7 system with four sensors is $640. And each box of four sensors is $240. And, no you cannot buy these individually.

I do not (yet) have insurance coverage for the Dexcom or the sensors. I'm hoping to start filing for this sometime during this week. From the Yahoo! diabetescgms group it sounds as if more companies are starting to cover the costs of this system. Unless you know that your insurer actually covers it, you need to consider the ongoing Dexcom sensor costs ($60 each for at least 7 days) before deciding to use one.

On the Yahoo! diabetescgms group, someone pointed out that CGMS users seem to be broken into 4 groups.

1. Those for whom the Minimed REAL time works well.
   
2. Those for whom the Dexcom 7 works well.
   
3. Those for whom either system works well, and
   
4. Those for whom neither works well.

Unless you try it out, you can't tell whether it will work for you. Contact your endo's office and see if they'll arrange a trial for you. You will need a prescription from your endo before you can get a trial. Originally I tried out the Dexcom 3 for a week, which allowed me to make a sensor change. I think this is crucial, so make sure you get to try out the Dexcom 7 for at least 9 days, ideally aim for 2 weeks. And make sure you get a copy of the software when you're doing the trial, the system is much better when you can actually use the (PC-only) software.

Sensor Insertion

Inserting a Dexcom sensor takes some work. With the Dexcom 7, the insertion is a lot less painful than with the Dexcom 3, but it's still tougher than for a pump. There's no spring-loaded inserter, you just have to jab it in. I continue to use it in my abdomen, but I know several people on the Yahoo! diabetescgms group have used arms and buttocks.

Once the sensor is inserted you connect the transmitter to the back of it. This combined unit is waterproof, and you can shower or swim with it and don't need to cover it in any way. The waterproofing is done by having the transmitter lock very firmly in place on the back of the sensor. You can only remove it using the plastic 'safety lock' that stops you from first accidentally inserting the sensor.

The Dexcom requires care and feeding. You need to calibrate it at least twice each day with a test taken using a OneTouch Ultra meter. Calibrating means you take a test with the OneTouch and then connect the OneTouch to the Dexcom via a supplied 5-foot cable, the synchronization takes about 10-15 seconds.

Alarming

You can change the alarm settings on the Dexcom with one setting for the low alarm (changeable in 10 mg/dL increments) and one for the high alarms (20 mg/dL increments). There's a hard-wired alarm that triggers at 55 mg/dL.

Except for the hard-wired one, the alarms only trigger each time the readings cross the boundary from normal to high or to low. So if your high alarm is set to 160 and the reading goes from 155 to 164, the alarm will trigger. If the Dexcom is reading 210 an hour later and the numbers never went below 160 you will not get another alarm. In the case of the hard-wired alarm, you'll get another one 15 minutes after the first.

The alarms can be loud. The first one is a loud buzz. If you miss it, or don't acknowledge it the next alarm is a loud buzz and noise. This happened to me yesterday and three co-workers in surrounding cubes wondered what it was and whether I was OK. So if you're easily embarrassed, watch out for this. In a recent webcast, the Dexcom CEO mentioned that the next generation Dexcom (no idea on dates) will have must more customizable alarms.

The Receiver

The receiver unit is fairly large, a little bigger than most of the insulin pumps available today. I usually carry it in my jeans pocket. It comes with a carrying case, but this is basically unusable. It sticks out very far from your belt and you can't connect the sync cable to it while it's in the case. And remember that it needs to be within 5 feet of the transmitter, so carrying it in a purse may not work.

The Dexcom receiver must be synchronized with a OneTouch Ultra meter at least twice a day. The recommendation is that you check your blood glucose using the meter before making decisions based on the Dexcom readings. In practice I probably test an average of 5 times a day, so don't expect a huge decrease in finger sticks because of the Dexcom. Note that Dexcom provided me with the OneTouch Ultra when I purchased my Dexcom 3 system, I assume they're still doing the same with the Dexcom 7. I also know that many insurance companies won't cover you for two makes of test strips. So if you're going to use the Dexcom, you're forced to switch from your current meter to the new one. The good news is that the Dexcom software will show you both the Dexcom system readings and the meter readings.

The picture below shows the 9-hour graph from the new and the old Dexcom receivers.


You need to charge the receiver about every 3 days, with the supplied charger. It's about the same size as my cellphone charger. I generally do this at night by plugging it in and then sleeping on top of the charging cable so the Dexcom can be beside me in bed. When sleeping I usually leave the Dexcom beside me because the receiver needs to be within 5 feet of the transmitter/sensor. And leaving it on my night stand means I may not hear it when it alarms.

With the Dexcom you'll get their new data management software. I complained loudly on this blog about the original DM software. The new version is much better with lots of useful and useablestatistics. You can also export the data as an XML file, or a comma-separated values (CSV) file which Excel can read.

What do I think about the Dexcom?

In April 2007, I described this as like having a superpower. And I still feel like this about it. My April A1C, just after starting the Dexcom, was 8.2% and my July A1C was 7.0%, a 15% reduction. I don't think I could have accomplished this without the Dexcom. It's also partially due to using Symlin more, and I really found the Dexcom invaluable to help me manage using Symlin.

For me, this has been a life-changing device. Diabetes management has become a lot easier all round. But there are also times when I want to throw it out the window. If I'm woken in the middle of the night (tonight) by a sensor alarm, it can be very annoying. If the usually smooth graph starts to have a lot of gaps in it for no reason that's also a pain.

But I'll stick with it, and I'm aiming for a further improvement in my A1C.

I hope this writeup helps you some in deciding about this device. Note: I still own shares in Dexcom. I try not to let that influence what I say in any of my posts.

Labels: CGM, devices, Dexcom, Dexcom SEVEN, diabetes, review

posted by Bernard @ 3:41 AM