Posted by on Thursday 31 December 2020

Hype or Hope? Dexcom, Tandem tSlim review and 2020 round-up

Wait... hang on... December 31st? That can't be right! Have we actually had a year this year? And how come any of the things that happened this year seem to have happened at least 18 months ago? No time has passed. But it has passed at a snail's pace. And at the same time we've all become accustomed to living completely different lives.

Doing a sort of round-up post for the year that never happened doesn't seem worthwhile. There are only so many times I can talk about avoiding a Zoom-based diabetes thing before I'm going to run out of waffle. Yes even me.

tldr; 2020 was a bit pants. But I really like the tSlim and Dex.

Tandem tSlim Insulin Pump
Tandem tSlim with Dexcom G6
Out with the old
I've been meaning to write a post or three about my experiences of the Dexcom G6 and my switch to the Tandem tSlim:x2 (and subsequent upgrade from Basal IQ to Control IQ) since the Summer, but for all sorts of reasons that series of posts never arrived. I have lots of pics of pump and graph cluttering up my phone that were apparently going to eloquently show something or other, but it's all so long ago now that I can't really remember what it was I was going to say.

I am self-funding Dexcom G6 sensors, and it was the first time I had used Dexcom. Such is the relentlessness of the positivity around Dex, that I think secretly I might have been hoping that I wouldn't find it all that special. 

I sprung for the 'starter pack' which gives an official 30-day's worth of coverage before I committed to going for the tSlim, so that if my body chemistry didn't get on with the Dex I could opt for Medtronic's MM670G (or similar) with self-funded Guardian G3 sensors. I had always got on well with Enlites and to some extent G3s too, and I was pretty sure that I would have got on well with the MM670G if that was what I'd gone for.

Inserting the Dexcom sensors was really straightforward, and initially I ran the sensors with my iPhone (not yet having taken the plunge on the pump). They restarted easily, and I didn't even have to faff about with unpeeling tapes and removing the transmitter thanks to these instructions. What really struck me though, was how well the factory calibrated G6 tracked fingerstick results from my Contour Next Link 2.4 meter (still my go-to BG meter). The first few days were uncanny. Spooky even. It didn't appear to be hype at all - generally Dexcom was reading only a few decimal points away from any fingerstick I took.

Dexcom G6 lagging a little against hypo recovery
Even a Dexcom G6 lags a little now and then
Reassuringly though, I did see a characteristic post-hypo-sensor-lag on about the 3rd day, where the Dex stubbornly continued bleating about low BG for 5-10 minutes after I was back above 4. So it was a regular CGM and not witchcraft after all. It was just that it was a really good CGM for me.

Joking aside, those early excellent matched pairs (against fingerstick checks) really helped me trust it as a new bit of kit though. 

And even better, while the factory calibration is excellent for me, and I've all but given up cross-checking with fingersticks, if I *need* to recalibrate the Dexcom G6 because it has drifted a little... I can! 

After a few weeks with the Dexcom I was confident to put in my request to switch to the Tandem tSlim when the warranty ran out on Threepio.

Switching to the Tandem tSlim:x2

I affectionately called my first insulin pump robot counterpart 'Artoo' (R2P2 - replacement to my pancreas #2), and kept with the Star Wars theme with my MM640G as 'Threepio'.  This bit of kit promised to be wiser and much more autonymous though, so I've taken to calling it HAL (hybrid automated loop), though of course it would be much funnier if a certain tangerine diabetic had made that joke, [affects creepily calm synthetic robot voice] "What are you doing Dave? I'm afraid I can't let you eat that biscuit..." etc.

Boxed Tandem tSlim
Staying in its box until I was trained up.

As all this was happening while the healthcare system was in some degree of chaos, and all those buzzwords like 'social distancing' were in full flow I wasn't sure how any kind of switchover was going to be able to happen - but in the end, in classic 2020 style I did my pump training via a video call having had the box of goodies delivered direct to my house.

I had a few weeks with Basal IQ before switching to the smarter Control IQ. Both worked well for me, and each have their own idiosyncracies. I have tried to do as little fiddling as possible, taking an initial 7 days to see how each got on when left to their own devices to try to learn what they are good at, and where they struggle. Also learning how to give them the right information to get the best results.

For those outside the Tandem bubble (seriously 2020? another word you've mangled?!), Basal IQ is Tandem's 'predictive low glucose suspend' algorithm, which stops basal insulin in order to try to reduce risk of hypos. Basal IQ is a little more responsive I feel than Smartguard on my MM640G. In that it can turn on and off more quickly, and doesn't have a minumim duration or enforced gap after it has completed. There was a major irritation for me when running the Basal IQ algorithm in that the tSlim moaned at you if you set a 0% TBR, though ot was more than happy to set one itself. Indeed, the tSlim got very grumpy if a TBR was set that was less than 50% of your lowest basal rate. A degree of warbling which was as unwanted as it was unnecessary.

This irritation was short lived though, as I soon upgraded to Control IQ. One of the nice things about the tSlim is that you can plug it into a computer and upgrade the software on the pump. Which means that if they release fancier, smarter, or even just mildly less irritating versions of the pump software, then you don't have to wait until 4 years have passed to take advantage. All I need now is to find the email address of the person to send my Helpful Suggestions to, for inclusion in the next release 😉


I guess I've been on the tSlim a little short of 6 months now, and I can honestly say that I am really glad I made the switch. I loved the MM640G, but the clunkiness of the Medtronic chassis, and some of the million-presses-UX-interface-tedium was wearing me down. Plus the newer G3 sensors were a bit more flaky and prone to overnight calibration requests for me. There are things about the tSlim I would hope would improve - not least the reservoir filling, which is every bit as fiddly as people say. Their reservoirs really need re-engineering so that the 'white dot' behaves more reliably (tSlim users will know what I mean). 

And what of results? Well I've not really that the nerd-energy for much actual data comparison, but going on gut feeling I would estimate that the tSlim has bumped my TIR (time spent between 4.0 and 9mmol/L) by somewhere between 5% and 15%. What used to be a really good week of results is rapidly becoming pretty normal. Control IQ still needs watching as it often responds a little later than I need, and it's not perhaps as 'hands off' as I was hoping it might be, but Control IQ really nails the little adjustments for me. It struggles with circumstances which are a bit wobblier, but it seems very good at optimising gentle drifts. Overnight with Sleep Mode has been spectacularly good. Almost no alarms, and almost always waking in the 5s to 7s.

Gotta be happy with 28/30 days above 80% TIR

It will be really interesting to see if this has had any kind of effect on my HbA1c, but to be honest, I increasingly find A1c a poor proxy for how I feel my diabetes management is going from month to month. It may still be seen as an important stat as far as research goes, but I'd far rather focus on the ebb, flow, and varying proportions of BG values that lie behind it. But that's another post I'll probably never get around to writing...

Here's hoping for a peaceful, healthy, happy and significantly more stable 2021 for us all.


  1. I am thrilled you have something that works for you. I use the Medtronic 770G and am looking forward to the 780g. I love great competition int he diabetes marketplace.

  2. Thanks for this Mike. Always good to read about the lived experiences rather than the marketing.

  3. There are occasions when I realise I haven't even thought about my diabetes for an hour or two. I look at the Tandem, it's been working hard, & my blood sugars fine. Absolutely priceless!

  4. This is an excellent post and really informative. I’m hoping to get my TIR to that extra 15% so this encouraging. I’m fearing the change to Dexcom AND Tandem though, all new tech. Currently on the Medtronic 640g and Libre 2, so dated 😂