Medtronic Guardian Connect Review - iPhone CGM in the cloud

Guardian Connect on iPhone, Guardian 2 on MM640G
and Contour Next Link 2.4

As some of you may know I've been lucky enough to be wearing Medtronic's new box of CGM tricks recently, and with nearly 4 weeks' wear under my belt and a few more days to go, it seems about time to post my thoughts about this new addition to the list of CGM options.

Ground rules
As I have been reflecting on my time using the Guardian Connect, a few things have stood out to me from the start. The first is that this is now the third continuous sensor system that I have tried. My first experience was Abbott's Libre flash glucose monitor (not strictly a CGM) and later, the MiniMed 640G sensor-augmented pump system which I trialled for 9 weeks in 2015. I mention this, because I think it has a significant effect on how I have responded to the Medtronic Guardian Connect. I am now no longer comparing 'no continuous data' to 'continuous data' which is, in itself, a huge change. Essentially you can take for granted that I am enjoying all the 'usual' benefits of access to continuous data - the ability to glance at your glucose level whenever you want to; overnight basal test type traces every morning, and trend and 'direction of travel' indicators. So what you get here is more me comparing the tiny details in user experience between the various systems, rather than being swept along by the benefits of CGM itself. I'm not sure if that makes this more or less helpful for anyone reading... but there it is.

Initial bewilderment
I don't know if you know anything about the Guardian Connect as you start reading this, or any other Medtronic diabetes technology for that matter - I mean why would you? But me... I'm on the inside, and that perhaps gave me certain expectations. I first chose a Medtronic Paradigm Veo which tantalisingly offered a 'low glucose suspend' if paired with the sensors that I never quite managed to afford. When I subsequently trialled the MM640G with it's souped-up 'predictive low glucose suspend' I think it's fair to say that for me, the results were extraordinary. Finally a piece of diabetes technology was actually proactively helping me out - dodging hypos automatically while I was blissfully unaware. So when I was first invited to trial the Guardian Connect I assumed that, of course, it would integrate with Medtronic pumps, SmartGuard and all the rest... Well... it doesn't.

So... CGM on iPhone... CGM in the cloud... sounds great! But what do you mean it doesn't link with SmartGuard? - I mean, wait... what?!
What I knew from the outset, was that the Medtronic Guardian Connect was a CGM that displayed sensor glucose readings on your iPhone, which sounds cool. And that it was Medtronic's 'CGM in the cloud' solution, which has very much been the buzzy new thing to have for a year or two. But I confess it completely threw me that this new CGM would not also communicate with my pump.

A new product line that explicitly doesn't offer the market-leading benefits of other devices in the same stable, while simultaneously offering all that trendy cloud-share-ness. Medtronic giveth, and they taketh away. Of course, Medtronic are keen to point out that the Guardian Connect was always designed as a standalone CGM (Medtronic have had a standalone Guardian CGM line for as long as I can remember). They say that this technology is intended for users of other pump brands, or people on multiple daily injections (MDI). Well... maybe. But I still find myself wondering whether a company would take this sort of decision if we were not living in a global marketplace with such complex approval mechanisms and timelines in different locations.

In a way I can sort of understand it from a technical perspective - my MM640G communicates on a completely different frequency to the bluetooth on my iPhone, so a transmitter would have to be able to send information to both devices. Would that increase transmitter size? I don't know - to be honest, I'm not really sure I care. All I know was that finding out that all the Guardian Connect iPhone-displaying-cloud-sharing juiciness came at the expense of SmartGuard was a real kicker.

The disappointment was particularly sharp when I discovered that people in the US have access to MiniMed Connect, which does link a MM530G, essentially a Veo with low glucose suspend, and transmits CGM to an app on iPhone or Android. Apparently MiniMed Connect is soon promised for the MM670G too - a newer pump than mine and not available in the UK. But all things? Approved in all markets? Available in all countries? Apparently not.

CGM displayed on your iPhone? Brilliant!
Having said all that, the idea of getting your sensor glucose sent to your iPhone is very appealing. I have very limited pocket space, and having to avoid scouring my phone screen to oblivion I need to keep keys and loose change in one pocket and my phone in another. So when using a Libre, with its separate reader, I have to squish reader and phone in the same pocket, and keep the reader in a little fluffy sock to keep them apart. Yes, you are right I am *such* a nerd. In short, having to carry a separate reader is a bit of a bind and the idea that I can use something I always carry with me anyway is hugely appealing.

Users of robot, rather than fruit-based smartphones may be wondering at this point whether Guardian Connect is available for Android? Well, at the time of writing, it isn't. And unfortunately I have no idea when, or if, an Android release might be available.

CGM in the cloud
The conspicuously 'on-trend' facility of the Guardian Connect is the way that it links to your Carelink account and can use a small slice of your phone's data connectivity to seamlessly upload your CGM data in the background. This gives you the opportunity of sharing your live CGM data with, for example, a partner, family member or housemate. This facility is particularly welcomed by parents of children with diabetes, who are able to keep an eye on things while their youngsters enjoy freedom to roam. Additionally Carelink allows you to set up text alerts, which will send an emergency message to a number or set of numbers if you do not respond to a low glucose alert. A potential lifesaver.

I think it is fair to say that personally I am not keen on Medtronic's Carelink platform. Particularly in its difficult current phase which is fraught with warnings of incompatibility if you dare to use current and up-to-date software. Medtronic promise that they are looking into upgrading their aging software, but evidence of progress or timeline remains frustratingly absent, aside from the recent release of Carelink Pro reports for everyone. The upshot of this lack of updatedness is that if you attempt to log-in to Carelink via iPhone you are greeted with a warning screen. However once you clear the warning, the live CGM data shows without problem. This easy access to sharing sensor glucose information has potentially powerful safety implications and would be a major encouragement, much as it is with Dexcom's Share, and the more homespun Nightscout options.

Getting set up
Before getting up close and personal with the new CGM technology, the first order of business was to download the Medtronic Guardian app from the App Store and hook it into my Medtronic Carelink account. For me, the next phase glamorously took place at the Diabeter clinic in Rotterdam, and involved pairing the Guardian Connect transmitter via Bluetooth to my iPhone. Screens in the Guardian app walked you through the pairing process, and an internet connection was required for the set-up. Once the ground work had been done it was simply a matter of inserting the Enlite sensor and waiting around 2 hours for the sensor to start-up. The Guardian Connect uses the same Enlite sensors as the MM640G system, but uses a completely different transmitter in order to communicate with your iPhone, iPad or iPod Touch.

Calibration 
Once the sensor has warmed-up you are prompted for a fingerstick calibration, which you enter into the app by pressing the blood-droplet 'calibration marker' top-right. This then shows a green circle around it which begins to count down, handily indicating the approximate amount of time before the next calibration is due. The precise timing being shown on the calibration entry screen itself. The calibration follows the familiar Enlite pattern of 2-6-12 hours after insertion and then approximately 12 hourly after that. The Guardian Connect also has the ability to request an additional calibration if it worries that things might be drifting slightly. My habit with Medtronic CGM has been to calibrate immediately before most meals (as long as they are not expected to be horrendously spiky ones). I find that 4 calibrations a day usually keeps an Enlite tracking very well for me. The usual guidance on calibration applies here - you should choose a time where, ideally, BG is within your target range, has been stable for 30 minutes or more and is expected to remain stable for the next 30 minutes. Avoiding calibrating when the Guardian app is showing up or down arrows really helps to keep the calibrations true. One nice thing about calibrations with Guardian Connect is that they are significantly faster than when I have used Enlite sensors with my pump. Connect calibrations are done and dusted within 5 minutes, while it can take 10-15 for my pump to finish calibrating.

Once or twice over my time with the Guardian Connect I have been prompted for an additional calibration overnight, which was initially confusing as I knew I had calibrated at around 11pm so should have been OK until morning. I suspect these were down to a less than ideal calibration earlier, eg one with BG moving or above target range.

A note for non-CGM users 
It is probably worth noting at this point for anyone reading who is considering using CGM for the first time the whole 'accuracy' question. People spend endless hours debating relative accuracies with CGM devices, and stressing or worrying if fingerstick and BG results are not identical all the time. In many ways, this is largely a waste of effort because a continuous sensor and plasma-calibrated blood glucose test strip are measuring completely different things - so they will never, can never show the same results all the time. It takes a while for glucose concentration in the fluid between tissue cells (that sensors measure) to come into line with capillary blood glucose. The differences are most noticeable when blood glucose is changing rapidly, and I particularly notice the lag when waiting for sensor glucose to show recovery after a dip into hypoglycaemia where the sensor may be 10 minutes or more behind 'now'. So you are well advised to decide to be fairly relaxed about any differences you see - providing, of course, that in general the information is within usable parameters.

For interest I am intending to give a suggestion of how I have found the tracking of Enlite sensors matches with fingerstick BG by taking a week of paired calibration readings. I've not got time to do that today, but I will add it here as soon as I can. My general feeling is that tracking between Enlites and fingersticks with the Guardian Connect is really very good indeed. And I trust it pretty much all the time. It's interesting to note how my frequency of fingerstick testing has fallen away while wearing sensors. Many days only checking fingersticks before meals, before bed, and before driving.

Update: Calibration and tracking vs Contour Next Link 2.4 
As promised I am editing this post to include some pairs of results between Enlite sensors on the Guardian Connect and my fingerstick BG meter (the Contour Next Link 2.4 USB that connects to my pump). Out of interest I have also done a comparison between the 'calibration' pairs for one of the sensors I have been using with my MM640G using the Guardian 2 transmitter - just because I was curious to see if there was any difference. Essentially I have looked at all the fingerstick BGs over the official 6 day life of the sensor that I used for calibration and compared them to the sensor glucose reading at the time. I should stress that this is not very scientific, and mostly for my own interest. The data set is pretty small (29 pairs for the Guardian Connect and 26 pairs for the MM640G). For what they are worth, here they are:

Medtronic Guardian Connect / Enlite results compared to Contour Next Link BG meter

	BG meter	Sensor	Avg +/- % (against BG meter reading)	Avg +/- mmol/L (against BG meter reading)
Average	8.4mmol/L	8.3mmol/L	7.8%	0.6
SD	2.8	2.5	5.7%	0.4
Distribution of readings
Number of readings where sensor higher			11	38%
Number of readings where sensor lower			16	55%
Number of readings equal			3	10%
Number of readings within 0.5mmol/L			13	45%

Medtronic MM640G / Guardian 2 / Enlite results compared to Contour Next Link BG meter

	BG meter	Sensor	Avg +/- % (against BG meter reading)	Avg +/- mmol/L (against BG meter reading)
Average	7.2mmol/L	7.2mmol/L	7.7%	0.6
SD	1.5	1.1	5.7%	0.5
Distribution of readings
Number of readings where sensor higher			12	46%
Number of readings where sensor lower			11	42%
Number of readings equal			4	15%
Number of readings within 0.5mmol/L			13	50%

My feeling is that these results are pretty much exactly the same between the two systems, which is reassuring, especially given the more varied results I was having on the days with the Guardian Connect with a higher average and wider SD (range of results). The MARD of less than 8% difference is above the expected performance of these sensors - I have always thought I must have lucky 'body chemistry' or whatever it is that means the sensors work better for some people than others. Effectively, it shows me that most of the time either of these systems will give me a result somewhere around 0.2-1.0mmol/L different from a fingerstick BG measurement (with potentially larger differences if my BG is moving rapidly, obviously). Around half the time, where my BG is just pottering along, sensor glucose and BG fingerstick are going to be less than 0.5mmol/L apart. And that is a level of accuracy I find easy to trust, and extremely useful in informing my diabetes management day to day.

Inside the app - traces, alerts and arrows
As a full CGM, the Guardian Connect offers both a rolling view of sensor glucose and audible/vibrate alerts if sensor glucose is, or is predicted to be, outside of a range you set. Today's sensor values are plotted as a graph and are viewable in 3hr, 6hr, 12hr and 24hr versions which each allow you to swipe back through previous time periods. Holding a finger over the graph reveals a scrolling pop-up of the value at that time. Additionally you can open the 'Now' menu to look back through previous day's sensor data.

Current sensor glucose is displayed above the graph, along with the menu and calibration icons. Where sensor glucose is changing more rapidly single, double or triple up or down arrows appear alongside the current sensor glucose reading.

Helpfully, when the sensor is coming close to expiry, or is running short of battery, you are alerted by icons on the main screen. Alternatively, you can always view the current details by looking in the menu screen.

The Guardian app also allows you to log insulin doses, carbs, blood glucose readings, activity or to make notes. The interface for adding and viewing each of these is pleasingly slick, but unfortunately you are required to log each value on a separate screen which would make regular use of them rather tiresome so I can't really see myself manually logging much additional detail using the app. The ability to add notes to provide context to what you are doing could be very handy though.

I was really pleased at the configurability of the alerts with the Connect. You can set both high and low alerts, along with additional alerts which are triggered anything from 10 minutes to 1 hour before your hard limit is expected to be reached if current sensor glucose trajectory continues. You can also set alerts where glucose is falling or rising particularly quickly. Snooze time allows you to customise how frequently you will be reminded of an alert condition - high and rise alert reminders can be set between 5 minutes and 3 hours while low and fall alerts can be set between 5 minutes and 1 hour. This probably all sounds needlessly confusing and granular in detail, but one of the challenges with CGM is to get good usable prompts without feeling nagged all the time, which makes the ability to precisely tailor both the mixture of alerts and their nag-ability really important.

You are also able to set an optional alert as a reminder that calibration is coming close to being due (rushing out of the house with no BG meter when a calibration comes due could make sensor glucose unavailable).

Not only that, but any and all of these alerts can be silenced at once with a single press on the iPhone's 'Control Centre' - more on that a little later.

Widget and app frustrations
Enabling Guardian Connect in the Notification centre can give you access to both alerts and a sensor glucose 'widget' on your phone's Lock Screen. Inexplicably though, the widget for a mmol/L Guardian Connect displays sensor glucose in mg/dl in the Lock Screen widget. Thankfully, as an app, this *should* be relatively easy for Medtronic to fix, but it still looks a little messy. Until the fix, users will just have to fall back on the, 'divide by 10, divide by 2, add 10%' mental acrobatics - unless their 18x table is reeeeeally good. As an example... 250 divide by 10 is 25. Half of 25 is 12.5 and then add 10% which makes 250mg/dl roughly 13.7mmol/L. Inside the app, alert states are shown by use of a coloured overlay panel.

Another frustration I had with the app, for all its smooth animation and solid build, was the total lack of any data analysis. I'm not sure whether this is something Medtronic have slated to add in future releases, but it seemed to me to be a significant missed opportunity not to have some sort of 7, 14, 30, 90 day sensor data overviews and number crunching. Or better still a pinch of Ambulatory Glucose Profiling to help make sense of that avalanche of data.

Enough with the interminable detail already - tell us what it was like to actually use!
Yes, sorry about that. Where were we...

Well... it's interesting. And actually I have been rather surprised by the experience. I think the only way to get my head around it is to list it as a series of pros and cons.

Pro - Less to carry, and very unobtrusive
Not having to carry an extra, separate reader has major benefits in terms of pocket space. We are used to carrying phones. We are used to glancing at them. No one would have any idea that you were interacting with your diabetes, even if you respond to or check an alert. Because that is what people do all the time in the modern world. There are a variety of tones used by the app, which indicate different things going on even before you get the phone out of your pocket. I kinda wish they had made the high and low alert tones slightly more varied. They do step up and down, but there is only around a semitone between the beginning and end and a quarter tone in between those, which all happens very rapidly. Occasionally I have heard the tone, but been unable to work out whether it was rising or falling. Of course it's not a real problem as it's only a glance at the screen to confirm - but I would have preferred that fraction of a second heads-up especially in circumstances where I might not be able to get my phone out for a minute or two.

Con - Now your phone is something else
Using the Guardian Connect has required me to make some adjustments in the way I use my phone - because now it is also my CGM receiver. I generally have my phone on silent, but I soon found that the single 'buzz' vibration alerts were too easy to miss, so I needed to put my phone's sounds on. Remember the single control centre command I mentioned to (helpfully) silence all CGM alerts if ever you needed to? It's the iPhone's 'Do not disturb' setting, which I have had running automatically overnight for several years. This prevented alerts sounding for ovenight hypoglycaemia, so I've had to de-activate its schedule and now activate it manually if I need to be notification-free for a time.

Pro - Phone battery life still reasonable
I am used to getting decent battery life out of my iPhones. Something like 3 days from a single charge - I suspect this makes me something of a rarity. I don't have a lot of push data notifications going on, and I deliberately restrict many of the usual battery hogs like background app refresh and screen brightness. I was a little concerned that the drip feed of continual data might suck all the life out of my battery, but while Guardian Connect has added a not insignificant demand on battery life I am still getting at least a full 2 days out of a single charge.

Con - battery charging
Of course, the flip side is that if you do run out of battery, it's no longer just your Twitter feed that you are missing - its your CGM and alerts too. And if your phone needs charging during the day, for all the time it's connected to the power socket you need to stay within about 9 feet of it to receive CGM alerts. This makes overnight phone charging a good basic approach.

Pro - gap filling
There have been times when my own peculiar charge cycle has got the better of me, and I've had to leave my phone charging on the side while I leave the room (or even the house) to do whatever. The neat trick of the Guardian Connect is that it stores several hours of data in the sensor, so that when you finally reconnect app and sensor the gaps are automatically filled in and your data remains intact. You don't get the missing alerts, of course. But at least you can look back over what has been going on while you've been away from your phone.

Con - Alert volume
Most of the time, when inside, the alerts are plenty loud enough. But the world is a busy, noisy place, and all too easily when walking outside I have missed both noise and vibrate alert. As a consequence I have tended to use the Guardian Connect a little like a Libre when out and about. Making sure I check it relatively frequently and not assuming the audible alerts would be able to cut through the hubbub. Sadly there's no way of making only the Connect alerts loud and leaving all your others at a quieter level, so it's a bit 'all or nothing'. I suppose as a fallback you could set a shorter alert snooze time so that you would get more repeated reminders of missed alerts.

Conclusions
I've not run any kind of analysis of BG numbers or hypoglycaemia frequency between Libre, MM640G/Smartguard and fingerstick-only as part of this review - quite frankly if you've made it this far I think you deserve a medal! I may try to find time to take a look at that in coming weeks with the data that are now safely stored in Carelink.

There is an awful lot to like about the Medtronic Guardian Connect. Despite my initial bewilderment, as a standalone product I think it sits very well among the current market and there is much to recommend it.

Medtronic get a bit twitchy at the idea of people who are trialling their kit restarting sensors, but having self-funded the same Enlites that this system uses since January I have found that I can get 12-14 days out of those with little if any apparent loss of performance. For anyone considering self-funding, the ability to restart to extend sensor life can be a make or break factor and I have no reason to believe that the Guardian Connect would behave differently to the Enlite's I've been using with my MM640G. Having said that I may just have lucky body-chemistry as I know from other user-groups that some people struggle to get more than 6 days out of an Enlite - so as ever YDMV.

My few weeks with the Medtronic Guardian Connect have given me very solid CGM performance, brilliantly flexible and tailorable alerts and while lacking the automation of Smartguard I get the feeling that the Guardian Connect has really helped me to keep my BGs in range, with very few hypos, and hardly any highs.

I've enjoyed using the system, though for a number of reasons I don't think it's one for me long-term.  I hope you've found this review interesting, please share your thoughts below.

Disclaimer: Medtronic offered me a trial of the Guardian Connect on loan with enough sensors to last 30 days. I have not been asked to write this or any other post about it, and have tried to accurately portray my likes and dislikes of the system. If I had thought it was utter rubbish I would have said so.