Friday, March 13, 2015

A mixed bag...


Abbott Libre Update


I keep receiving private questions about the technical aspects of the Abbott Freestyle Libre. Yes, I know a bit more than what I have posted publicly, but what I know isn't really earth shattering. If I come up with something that is new, genuinely useful and can be shared publicly, I'll be sure to report it here. But right now, our family in France seems to be experiencing... difficulties in obtaining sensors. I am not reading too much into this (update 14/03/2015 - apparently resolved - could have been an ordering snafu as a few other users have experienced). A couple of the blog readers have offered to send me sensors so I could go on in my investigations and I thank them for that: I would have accepted if I thought I could make significant progress that could be of use to the T1D community but, at this point, this is unlikely.

As far as the performance of the sensor is concerned, most of the sensors we have used were well behaved and performed in line with our previous experiments, in other words, much better than the Dexcom G4 (non AP) sensor.

Here is one trace from a recent tennis game where, again, you can clearly see both sensors in action and the Dexcom's algorithm delay is clearly visible.


We also had a weirdly defective sensor that was always too low between a certain threshold but behaved perfectly in the ranges above that threshold. In a way, that was one of our most interesting sensors as far as providing technical insights was concerned. This "lowish" behavior is quite visible in the "official" chart below.


Acute DKA and death.


This being said, Abbott's PR department seems to currently have bigger worries in terms of image and possible financial damage with this unfortunate story.

From what we know of the technical issue, it seems that someone somehow either forgot to enter or or failed recognize the proper calibration curve of the strips used in a third party device (Omnipod). At first sight, this looks like a software/firmware bug that had fatal and extremely unfortunate consequences... I won't comment in details about this story but regardless of the outcome of the complaint, the main lesson for us is quite clear: do not blindly trust the technology. A lot of people seem to assume, possibly somewhat misled by excessively optimistic advertisements, that devices should behave flawlessly. That's not the case: technology fails, especially in a cutting edge field where it meets biological constraints and human psychology. Abundant information doesn't necessarily means abundant truth. Keep thinking folks. The diabetes technology isn't nearly as accurate as pocket calculators have been for 40 years. The time to forget mental arithmetic has not come yet.

I was also surprised by the discussions of that case that I saw in the Internet forums: a lot of PWDs seemed to be unaware that DKA can kill and kill quickly (another example here). This is probably something I'll get back to as well as my son is just recovering from a severe pharyngitis that had, for a few days, a spectacular impact on his blood glucose levels and treatment. An unfortunate situation but a perfect illustration of why and how, if left unchecked, a fairly standard situation can become dangerous.

Dexcom sensor update


The current lack of Libre sensors drives us back to Dexcom... Unfortunately, the news haven't been too good on that front either. We either have been extremely unlucky or Dexcom is experiencing some difficulties in keeping up with the demand. Our last sensors set contained one sensor that, despite a correct insertion, kept reporting "0" as raw values (and of course failed at once from the point of view of the Dexcom receiver), another that kept reporting an impossibly high and stable raw value. That one was also reported as failed by the receiver but it took a bit longer.

And finally, the icing on the cake, if I dare say so, was this inserter... It apparently came without a needle and a sensing wire, its guide tube floating almost freely in the upper part of the device


This was a bit too much, even for a careless guy such as myself, and I did request a replacement this time. As I understand it, the replacement policy applied by Dexcom's distributors isn't as tolerant as Dexcom's own policy and I had not even bothered complaining until now. I don't blame them as I suppose they might be a bit more constrained by Dexcom's business terms. In my case, the exchange went without a hitch and a new sensor was sent as soon as I complained. Our local distributor has, so far, done a perfect job in terms of deliveries.

But there are more problems on the horizon. I was told a few weeks ago that we would not get the 505 algorithm update in Europe because Dexcom would soon be releasing exciting new products. Well, the exciting new products were indeed released but... we are unlikely to get them either (at least officially). This probably boils down partly to the time and effort required to get approval (eventhough Dexcom did get pediatric approval in Europe before US) and to the possibly inherently illegal strings attached to their data sharing plan.

Caught between a rock and a hard place: xDrip to the rescue.


This leaves us caught between a rock (slow approval/availability for Dexcom's new products) and a hard place (apparent obstacles in ordering sensors from Abbott)... To put it bluntly, once you have used well behaved Libre sensors, it is extremely hard to remain satisfied with the performance of the G4 non-AP system. (in a way, given some of the issues I have with Abbott's behavior, it hurts a bit to report that, but I strive to remain objective).

Are we in a hopeless situation? Fortunately not. xDrip is a promising open source project that offers, at least partly, a solution to our problem. Our initial tests seem to show that its performance is closer to a good Libre sensor (and to the 505 AP Dexcom algorithm should be) than the standard G4 non AP system. It also offers all the advantages of a full CGM setup (constant monitoring, alerts, remote uploads). I suspect it will be somewhat constrained in terms of speed by the sparse 5 min Dexcom sampling, but we'll see. That project probably isn't for everyone and is not, for those who live on the other side of the ocean, FDA approved. Unlike the standard version of Nightscout, it goes a bit further than the simple replication of the Dexcom data by using its own calibration curve. If that scares you, even slightly, stay away from it. It is worth noting however that sensor calibration is a very common technique in analytical chemistry: while it may seem to be rocket science, it definitely is not as it only requires high-school (or possibly 1st year college depending on where you live) mathematical techniques. That simplicity means that it easy to understand and analyze.

That's all for today. Stay tuned for more.

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