Friday, October 3, 2014

Going CGM

Maintaining a 8-10 hours per week tennis training schedule, dealing with delayed hypos, checking every meal and trying not to sacrifice diabetes control implies finger pricks. Tons of them. Until March, we were averaging 10+ tests each day. Long tennis games would often require 8+ tests. Obviously, we couldn't go on like this.

As soon as Maxime had been diagnosed, I hit the Internet looking for solutions, tips and tricks that would improve is diabetic life. One of the first things I discovered was that Continous Glucose Monitoring devices existed (CGMs). These things are expensive: you typically need a receiver (approximately 900 EUR), a transmitter that should last 6 months (approximately 300 EUR) and one 75 EUR sensor each week. Assuming you run everything by the book and change your CGM every two years, you end up with a significant bill

  • 1 receiver 900 EUR
  • 4 transmitters 1200 EUR
  • 104 sensors 7800 EUR

or roughly 4950 EUR per year.

In practice, sensors can be run for a couple of weeks on average and that lowers the cost a bit, to 3000 EUR per year. This is still a significant amount of money that is, of course, "out of pocket" in our almost free but strained European social security systems (although this recently changed in Belgium for kids on a pump).

While there was no therapeutic obligation (very good control at 5.3 and 5.5% HbA1c), the damage done to Max's fingers and the mental fatigue induced by the constant stress of keeping sparsely sampled curves in our minds at all time decided us to give CGM a try.

We chose to go for the Dexcom G4 system which seemed to have good reputation on the Net but was also described as one of the two best performing CGM in artificial pancreas studies (here for example http://www.ncbi.nlm.nih.gov/pubmed/24876423.)

There's a lot to say about CGM, delays between the interstitial glucose they measure and the actual blood glucose level, their precision, calibration strategies and other pitfalls. But let's not go too fast...

One of the first thing I did was to write a small program that checked if the average of the results given by the CGM was roughly equivalent to the average results of the blood tester we used. I was pleased by the result. As you can see from the numbers below, on average, the CGM tracks quite closely the results we would have had from the blood glucose finger pricks, including tests not used for calibration. Those charts and stats reassured me fully: the CGM could be trusted for global goals in the long run.

CGM vs BG Tester - average basic stats
The average glucose values are quite close and so is the standard deviation and the profile do match closely. One could nitpick about the bigger standard deviation observed with the BG tester, but that's explainable by the fact that we check more often when Max is a bit lower or higher than usual.

Note 1: the hole in the July CGM data corresponds to a period where the CGM wasn't used. Hot weather and abundant sweat are sometimes difficult to deal with.

Note 2: the May-June hole in the BG tester data corresponds to a period we were using another BG tester. Adding that second BG tester data does not alter the overall result.



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