Why I can't wait for the new Dexcom

Some time ago I mentioned the upcoming release new version of the Dexcom. It will let you calibrate the system without needing that darn cable. You can also use any blood glucose meter. Dexcom calls this 'open coding' and it is meant to be available around March 2008.

There two big advantages to this small change:

• You don't need to carry the darn cable anymore
  
• You can calibrate the Dexcom using any blood glucose meter

So why do I think this is such a big deal? Bear with me while I give a long explanation.

Last year I saw my A1C levels improve from April (just after I'd started the Dexcom) to July. But in October my A1C was back over 8.0%. That means my average blood sugar was around 200 mg/dL. However the Dexcom software said my average blood glucose was around 152 mg/dL, equivalent to an A1C of about 6.5%. That's a huge difference. One of the numbers must be wrong...or could they both be right?

Here's how I think the problem arises.

I calibrate my Dexcom with a OneTouch Ultra blood glucose meter. Like most meters, it's accuracy is about plus or minus 20%. (This is what is 'acceptable' according to standards for blood glucose meters.) So if it reports my blood glucose(BG) was 150, it's actually somewhere in the range of 120 to 180 mg/dL.

When I calibrate the Dexcom with it, the Dexcom uses that information when it calculates as my BG values. From experience I know that the Dexcom has a tendency to slightly low ball the numbers. So when it reports my BG at 80 mg/dL, my meter is likely to say it's around 95 (effective range 76 to 114). Result - I'm using a meter with a lowish accuracy to calibrate a continuous glucose monitor that's also got a lowish accuracy.

Perhaps my A1C is high, because I'm carefully using inaccurate systems to keep it within a tight range. It's just the wrong range!

I was given a WaveSense meter last year to review. I liked it a lot, it has a really good design and is easy to use. I even put a YouTube video up that showed the WaveSense in action. The folks had clearly put a lot of thought into the meter.

The big thing about WaveSense meters is their accuracy. They certainly conform to ISO standards, all readings are within 20% of the true value. But with these meters, most readings are also within 10% of the real number. So if it reports my BG level as 150, then it's almost definitely between the range 135 to 165 mg/dL. That's way better, to my mind, than the 120 to 180 range for other meters

One thing I noticed whenever I used the WaveSense is that it would frequently give me a higher reading than the other meter I was using at the time. At the time I thought this was strange. Now looking back on it I realize that this is probably because of the WaveSense's better accuracy. The other meter was giving me a slightly lower, but less accurate, reading. Which made me correct with less insulin because I thought my BG was closer to the target that it really was.

When Dexcom allows me to use any meter I want to, I'm not going hesitate. I'll switch right over to the WaveSense meter that I've been using as a backup ever since I got it. That'll give me a third advantage: better A1C results, I hope!

I can't wait.

Labels: A1C, accuracy, Dexcom, wavesense

posted by Bernard @ 10:21 AM