“What’s CGM?” you may ask. Some new User Experience methodology, perhaps, or a research group exploring Web Science through some novel lens? No, CGM is Continuous Glucose Monitoring, whereby a device is implanted to get a stream of data representing your blood sugar level. As someone with type 1 diabetes, I’ve spent an inordinate amount of time in the past decade pricking my fingertips to extract a little blood and check my level.

Recently, I decided it was time to branch out and try CGM. I opted for the Freestyle Libre as a relatively lightweight approach. You wear a sensor, which lasts for two weeks, in the back of your arm. You can scan it as often as you like to get an estimate of the current sugar level, and (usually) a guess as to if and how that level is changing (an arrow shows whether the machine estimates the number is stable, or going up or down).

It’s definitely a different experience. Beforehand I found accounts online varying from users reporting that the sensor hurt too much to wear to others saying they didn’t feel it at all. Lucky for me, I’m nearer the latter end of the spectrum: my arm feels uncomfortable for a day or two after application, but that’s about it so far.

The sensor comes with an ‘applicator’ that you push against your arm; the applicator slams the sensor in at high speed. There’s a little needle (which seems to be plastic or some composite) that sits in the arm, and a very, very strong adhesive holds the sensor on. In fact I found removing the sensor after a fortnight far more uncomfortable than applying it in the first place. I’m only on my second sensor as I write this, so it’ll be interesting to see whether that experience will vary.

In any case, for me the discomfort is worth it: the freedom of being able to check my glucose at any time is amazing, especially when I’m out and about. With the old method, I had to prick my finger and squeeze enough blood out onto a test strip; now, thanks to this technology, I just wave the device at my arm, through clothes. I can check my sugars while walking in the Vancouver rain!

It’s less accurate than the fingerprick approach (the error bars are around 20%, compared with 10% for fingerprick checks), so I am still extracting blood if for example the sensor gives a reading that doesn’t tally with how I feel.

One gotcha is that if I check too frequently I can be tempted to intervene when I should not: for instance, my sugar level rises after a meal so it may be tempting to take insulin to reduce a high when in fact the insulin I already took is about to kick in.

Here’s the frequency of my recent fingerprick checks:

Date Tests
Feb-01 7
Feb-02 8
Feb-03 12
Feb-04 6
Feb-05 4
Feb-06 4
Feb-07 2
Feb-08 0
Feb-09 0
Feb-10 0
Feb-11 2
Feb-12 0
Feb-13 1
Feb-14 0
Feb-15 1
Feb-16 0
Feb-17 0
Feb-18 1

1st and 2nd February were my last two days pre-CGM, where I’d say I did an average number of fingerprick checks. At mid-morning on 3rd February I started using the Libre, so the 12 checks that day comprise some normal night time and breakfast time checks pre-Libre, then a tonne of extra checks as I verified what the sensor was telling me. My rate of fingerprick checks slowly tails off over the next few days as I get a feel for the device, then drops right down to 0-2 checks a day (verification of sensor readings that I don’t trust).

Only ten days into wearing the Libre sensor, I caught myself thinking of fingerprick checking of blood sugar as an old-school and rather uncivilised approach! How quickly we adapt.