A continuous glucose monitor (CGM) uses a very thin gauge wire to sense interstitial fluid as a proxy for blood sugar.

My kids have tried Dexcom G4 CGMs a couple years ago. The G4 was never approved to dose insulin directly off the CGM reported value, we would confirm with a finger prick before dosing a correction. The G4 also required “calibration” where you would type in the reading from a finger stick and it would shift the curve a bit in that direction if it was off base.

We would routinely find the G4 reporting numbers up to 100 points off, or simply dropping out and reporting “???” for hours at a time. Bad or unreliable data being worse than no data, we discontinued using the G4.

The Dexcom G5 kept the same sensor but switched the transmitter (which connects to the sensor and sits on your body) to use standard Bluetooth to communicate the glucose readings. This is when Nightscout was really able to step in and intercept the glucose data and do neat things like put it in the cloud so you could watch your kids’ blood sugar throughout the day. And with the addition of a programmable pump, also try to build a “closed-loop” system which constantly adjusts basal insulin dosages to react to highs and lows.

The problem is the underlying sensor of the G5 was still not approved for direct dosing, a finger-stick still being the only method accurate enough. You don’t want to dose to correct a 250 blood sugar level and then discover you actually were 150 all along and now potentially heading for a dangerous low.

Early this year we started buying Freestyle Libre sensors which use a NFC reader to poll the latest readings on demand. This is a less ideal method because it can’t independently alert you of an impending high or low without you actively swiping the reader up against the sensor on your arm. Accuracy was significantly better (reading would often be within 15-30 points, and we didn’t see any that were more than 60 points off from a finger stick reading) and there were a couple times when it would stop reporting data but dropouts where much less common than what we experienced with the G4.

Fast forward to last month when we got brand new Dexcom G6 CGMs. These are FDA approved to dose directly off the readout, and the accuracy is frankly unbelievable. We have regularly had finger sticks exactly match the CGM display, and even finger sticks have variation when you test multiple times back-to-back. The G6 does not require daily calibration (although you have the option if you find the numbers are off). It is not perfect, and once we did find it was 40 points off, but after 60 days of use my experience is that with the G6 we have finally arrived at a stable, trustworthy, reliable CGM which I would feel comfortable driving a closed loop system.

The only failing I have with the G6 is that we were promised it would work directly with an Apple Watch running the Dexcom app and syncing with the sensor over Bluetooth. In fact, as of now, a full fledged iPhone is required to pull data from the sensor, and then it can relay from the phone to the watch. I’m told that the FDA is pending approval of a stand-alone Watch operation, which would be exceedingly useful in my case. The goal is for the kids to wear LTE Watches which can read from their sensor directly and push glucose data to the cloud for us to watch on our phones. This would mean just the $5/mo cost to add a Watch to the plan versus having to add lines and gives full fledged iPhones to the kids in order to track their numbers remotely.

Both our kids use OmniPods as their insulin pumps, which AFAIK have not been hacked yet to allow 3rd party control of the pump. OmniPod is a self enclosed pump which sticks on your arm an auto-injects a cannula, and you control it wirelessly with a dedicated remote which is like a 1990s PDA. OmniPod has an ongoing study with their next-gen “Horizon” product which adds Bluetooth control and interfaces with the Dexcom G6 to automatically adjust basal rates.

Last thing I’ll mention is that this is not by any means an “artificial pancreas”. Even with a closed loop system you still must bolus (administer insulin) before meals in the correct ratio based on the number of carbs, and the glycemic index (speed of absorption). The closed loop is more rather a slight adjustment in the baseline insulin which is being automatically dosed every few minutes to cover your basal metabolic rate. If the CGM sees you are high or low, a closed loop system will temporarily increase or decrease the basal insulin rate to try to subtly move the needle so-to-speak and bring blood sugar back in range. This works best overnight when no new carbs are being eaten and blood sugar is usually more stable. So the idea is with a closed loop you are more likely to wake up with a blood sugar around 100 because it’s been working to gently bring you to that level all night long.

As the article states, this means a better nights sleep for both parent and child :-)