The last time I wrote anything interesting about Abbott’s flash glucose monitor (don’t call it a CGM) was when I compared it with the underwhelming Dexcom G6. I thought it would be a good time to provide an update, what with Abbott sending a number of email reminding you to update their FreeStyle LibreLink app in the past couple of weeks.
First of all, there’s the matter of supplies. Back in January, I decided to test Dexcom’s CGM because Abbott’s supply issues bit me in the backside, as I could not get new sensors to keep up with my usage — particularly as the more active life in London with my girlfriend meant losing a couple more sensors to mistakes, such as bumping into the doorframe. For a while, you could only buy three sensors every 25 days, and even then, sometimes the lead time to fulfill the order would be over a week; nowadays this appears to be much better, and the time limit for the orders was removed recently.
Since I was not particularly thrilled to switch to the Dexcom G6, I had to find a way around these limits, beside counting on the two extra sensors I “gained” by not using the Libre for a month. Luck was that a friend of my girlfriend found the Libre sensors on sale in a brick-and-mortar store in Sharjah, and managed to send me six of them. The store had no limits on how many sensors you could buy, despite the FreeStyle UK website only allowing orders of three at most, and only to already-established customers.
The UAE-bought sensors are effectively the same as the British ones, with the same manufacturing information printed on them, and even similar enough lot numbers. The most visible difference is that the two alcohol-soaked tissues, provided for cleaning the insertion point, are missing.
The other difference is not visible in the packaging, or indeed on the hardware itself: the sensors are region-locked. Or maybe we should say that the app is. As it is, my (UK) FreeStyle LibreLink install did not want to set up the UAE-bought sensors. The reader device had no such concern and both initialised and read them just fine. I was originally a bit concerned and spot-checked the values with fingersticks, but it looked like there was no issue with the sensors at all.
I’ve been wondering just how much the supply problem connects with the region locking. Or just how fine-grained the region locking is: my Irish sensors worked perfectly fine with the UK app, although by that point, the app was not available in Ireland at all. But possibly all of these problems are gone.
Now, to go back to Abbott’s email messages to update their LibreLink app. The reason for this update is not much about the UI of the app itself – although that did change a bit, in subtle and annoying ways – but rather a change in their algorithm for turning the sensors’ readings into a human-understandable blood glucose reading. The “curve”, as it’s sometimes referred to. It’s important to note that what the sensors communicate with either the app or the reader device are not “fully cooked” blood sugar readings, but rather a set of different sensors reading, and that the app and reader will then apply some formulas to provide an equivalent reading to a fingerstick.
Much more interesting to me, in the announcement of the new curve, is that they also suggest users to update the firmware of reader devices to make use of the new fine-tuned algorithm. This is interesting because it makes the FreeStyle Libre the first glucometer with an upgradeable firmware. I have not actually run the update myself, yet. It needs to be done just before changing the sensor, as the reader will forget about its last sensor at that point, and I’m a bit worried that it might not work with UAE-bought sensors anymore after that. So I’m instead waiting to finish the supply of those sensors, and maybe get another one later to test after the update.
I also want to try to get a usbmon trace of the whole procedure for the firmware update. I’m not sure when Abbott will ever publish another update for the reader, but at least starting collecting the protocol would be interesting. Once I do that, you can expect another blog post on the topic.
And as a final note, glucometerutils is being updated as I type this to support reading and setting patient names. While I would not suggest people to use that field for their own personal glucometer, I thought it would be nice to provide the building block for more doctor-focused apps to be built out of it. As a reminder, the code is released under the MIT license, because using it to build something else is a primary focus of it — we need better tooling for glucometers, and not just in the Free Software world, but in the world in general!